"FANCY" BLUE DIAMONDS. 5. Blue diamonds are usually of very pale bluish or violet tint. A few deeper blue stones are seen occasionally as "fancy" diamonds. These are seldom as deep blue as pale sapphires. Even the famous Hope Blue Diamond, a stone of about forty-four carats and of great value, is said to be too light in color to be considered a fine sapphire blue. Some of the deeper blue diamonds have a steely cast. The so-called blue-white stones are rarely blue in their body color, but rather are so nearly white that the blue parts of the spectra which they produce are very much in evidence, thus causing them to face up blue. There is little likelihood of mistaking a bluish diamond for any other stone on account of the "fire" and the adamantine luster of the diamond.

6. Blue zircon, however, has nearly adamantine luster and considerable fire. The color is usually sky blue. Such stones are seldom met with in the trade.

For a more detailed account of the various blue stones see G. F. Herbert-Smith's Gem-Stones, as follows:

For sapphires, pp. 172-173, 176, 182; for spinel, pp. 203, 204, 205; for tourmaline, pp. 220, 221, 223; for topaz, pp. 198, 200, 201; for diamond, pp. 130, 136, 170, and for zircon, pp. 229, 231.



LESSON XIV

COLOR—Concluded

PINK, PURPLE, BROWN, AND COLORLESS STONES

PINK STONES. Pink stones are yielded by (1) corundum (pink sapphire), (2) spinel (balas ruby), (3) tourmaline (rubellite), (4) true topaz (almost always artificially altered), (5) beryl (morganite), (6) spodumene (kunzite), and (7) quartz (rose-quartz).

These pink minerals are not easily differentiated by color alone, as the depth and quality of the pink vary greatly in different specimens of the same mineral and in the different minerals. There is dichroism in the cases of pink sapphire, pink tourmaline (strong), pink topaz (strong), pink beryl (less pronounced), and kunzite (very marked and with a yellowish tint in some directions that contrasts with the beautiful violet tint in another direction in the crystal). Pink quartz is almost always milky, and shows little dichroism. Pink spinel is without dichroism, being singly refracting. Hardness and specific gravity tests will best serve to distinguish pink stones from each other. The color alone is not a safe guide.

PURPLE STONES. Among the mineral species that furnish purple stones, (1) quartz is pre-eminent in the fineness of the purple color. Such purple stones are, of course, known as amethysts. After quartz come (2) corundum (Oriental amethyst), (3) spinel (almandine spinel), (4) garnet (almandine), and (5) spodumene (variety kunzite).

The purple of the amethyst varies from the palest tints to the full rich velvety grape-purple of the so-called Siberian amethysts. The latter are of a reddish purple (sometimes almost red) by artificial light, but of a fine violet by daylight. No other purple stone approaches them in fineness of coloring, so that here we have a real distinction based on color alone. If the purple is paler, however, one cannot be sure of the mineral by its color. Purple corundum (Oriental amethyst) is seldom as fine in color as ordinary amethyst, and never as fine as the best amethyst. It is usually of a redder purple, and by artificial light is almost ruby-like in its color.

Purple spinels are singly refracting, and lack dichroism, and hence lack variety of color. Almandine garnets also show no dichroism and lack variety of color. The garnets are, as a rule, apt to be more dense in color than the spinels.

Purple spodumene (kunzite) is pinkish to lilac in shade—usually pale, unless in large masses, and it shows very marked dichroism. A yellowish cast of color may be seen in certain directions in it also, which will aid in distinguishing it from other purple stones.

BROWN STONES. (1) Diamond, (2) garnet, (3) tourmaline, and (4) zircon furnish the principal brown stones.

Diamond, when brown, unless of a deep and pleasing color, is very undesirable, as it absorbs much light, and appears dirty by daylight and dark and sleepy by artificial light. When of a fine golden brown a diamond may have considerable value as a "fancy" stone. Such "golden fancies" can be distinguished from other brown stones (except perhaps brown zircons) by their adamantine luster, and their prismatic play or "fire."

Brown garnet (hessonite or cinnamon stone), sometimes wrongly called hyacinth in the trade, is of a deep reddish-brown color. Usually the interior structure, as seen under a lens, is streaky, having a sort of mixed oil and water appearance.

Brown tourmaline is sometimes very pleasing in color. It is deep in shade, less red than cinnamon stone, and with marked dichroism, which both brown diamond and brown garnet lack.

Brown zircon, while lacking dichroism, is frequently rich and pleasing in shade, and when well cut is very snappy, the luster being almost adamantine, the dispersion being large, and the refractive index high. It is useless to deny that by the unaided eye one might be deceived into thinking that a fine brown zircon was a brown diamond. However, the large double refraction of the zircon easily distinguishes it from diamond (use the sunlight-card method or look for the doubling of the edges of the rear facets as seen through the table). The relative softness (7-1/2) also easily differentiates it from diamond.

COLORLESS STONES. Few colorless stones other than diamond, white sapphire (chiefly scientific), and quartz are seen in the trade. Colorless true topaz is sometimes sold and artificially whitened zircon (jargoon) is also occasionally met with. Beryl of very light green tint or even entirely colorless may also be seen at times.

Such colorless stones must of course be distinguished by properties other than color. They are mentioned here merely that the learner may be aware of what varieties of gem minerals occur in the colorless condition, and that all these minerals also occur with color in their more usual forms. This does not even except the diamond, which is rarely truly colorless.



LESSON XV

HOW TO TELL SCIENTIFIC STONES FROM NATURAL GEMS

It should be said first that the only true scientific or synthetic stones on the market are those having the composition and properties of corundum, that is to say, the ruby and the several color varieties of sapphire, as blue, pink, yellow, and white. There is also a greenish stone that appears reddish by artificial light, which is called scientific alexandrite but which has, however, the composition and properties of the corundum gems rather than those of true alexandrite. All so-called "scientific emeralds" have proved to be either of paste of one sort or another, or else triplets having a top and a back of some inexpensive but hard stone of pale color, and a central slice of deep green glass, the three pieces being cemented together so skillfully that the junctions frequently escape any but a very careful examination with a lens.

ALL SCIENTIFIC STONES ARE CORUNDUM GEMS. Now the fact that all true scientific stones are corundum gems makes their determination fairly simple on the following basis: Among the considerable number of corundum gems of nature, whether ruby or sapphire of various colors, there is seldom found one that is entirely free from defects. Almost always, even in what are regarded as fine specimens, one will easily find with a glass, defects in the crystallization. Moreover these defects are characteristic of the corundum gems.

The scientific corundum gems, however, never have these specific defects. Hence the surest and simplest way of distinguishing between the two kinds of stones is to acquaint oneself with the typical defects of natural corundum gems, and then to look for such defects in any specimen of ruby or sapphire that is in question.

While a description of some of the most common of the typical defects of rubies and sapphires is to follow, the jeweler, who may not yet be familiar with them by actual experience, owes it to himself and to his customers to acquaint himself at first hand with the natural defects of such material, which he is always in a position to do through the courtesy of representatives of houses dealing in precious stones, if he himself does not carry such material in stock.

TYPICAL DEFECTS OF NATURAL CORUNDUM GEMS. Perhaps the most common of the defects of natural corundum gems is the peculiar appearance known as "silk." This is best seen when a strong light is allowed to stream through the stone at right angles to the observer's line of sight. Sets of fine, straight, parallel lines will be seen, and these will frequently meet other sets of similar lines at an angle of 120 degrees (like the angle at which the sides of a regular hexagon meet) or the lines may cross each other at that angle or at an angle of 60 degrees (the supplement of 120 degrees). Such straight parallel lines are never seen in scientific stones, and their presence may be taken to indicate positively that the stone having them is a natural stone. In fine specimens of natural ruby or sapphire such lines will be few and difficult to find, but in some position or other they will usually be found if the search is even as careful as that which one would habitually employ in looking for defects in a diamond. In the vast majority of cases no such careful search will be required to locate "silk" in natural rubies, and if a stone that is apparently a ruby is free from such defects it is almost a foregone conclusion it is a scientific stone.

Another common type of defect in corundum gems is the occurrence of patches of milky cloudiness within the material. A little actual acquaintance with the appearance of this sort of defect in natural stones will make it easy to distinguish from the occasional cloudiness found in scientific stones, which latter cloudiness is due to the presence of swarms of minute gas bubbles. These tiny bubbles can be seen under a high power lens, and this suggests a third feature that may be used to tell whether one has a natural stone or not.

Natural rubies and sapphires, like scientific ones, frequently contain bubbles, but these are always angular in the natural stones, while those of the scientific stones are generally round or rounding, never angular.

To sum up the suggestions already presented it may be said that, since natural and scientific corundum gems are composed of essentially the same material, and have identically the same physical and chemical properties, and frequently very closely resemble each other in color, it is necessary to have recourse to some other means of distinguishing between them. The best and simplest means for those who are acquainted with the structural defects common to natural corundum gems is to seek for such defects in any specimen that is in question, and if no such defects can be found, to be very sceptical as to the naturalness of the specimen, inasmuch as perfect corundum gems are very rare in nature, and when of fine color command exceedingly high prices. No jeweler can afford to risk his reputation for knowledge and for integrity by selling as a natural stone any gem which does not possess the minor defects common to practically all corundum gems.

STRUCTURAL DEFECTS OF SCIENTIFIC STONES. So far our tests have been mostly negative. It was said, however, that spherical bubbles sometimes appear in scientific gems. Another characteristic structural defect of practically every scientific gem may be utilized to distinguish them. As is well known, the rough material is formed in boules or pear-shaped drops under an inverted blowpipe. The powdered material is fed in with one of the gases and passes through the flame, melting as it goes, and then accumulating and crystallizing below as a boule. The top or head of this boule is rounding from the start, and hence the successive layers of material gather in thin curved zones. The color and structure of these successive zones are not perfectly uniform, hence when cut stones are made from the boules these curving parallel layers may be seen within by the use of a good lens, especially if the cut stone is held in a strong crossing light, as was suggested when directions were given above as to the best way to look for "silk" in a natural stone.

Owing to the shape of a well cut stone it is sometimes difficult to get light through the material, yet by turning the stone repeatedly, some position will be found in which the curving parallel striae can be seen. They are easily seen in scientific ruby, less easily in dark blue sapphire, but still they can be found on close search. In the light colored stones and in white sapphire, the difficulty is greater, as there are no color variations in the latter case. However, the value of white sapphire is so slight, whether natural or artificial, that it is a matter of but little moment, and what has already been said as to natural defects, applies to white sapphire as well as to the colored varieties, and absolutely clear and perfect natural white sapphire is rare.

One more distinguishing mark of the scientific stones may be added to give full measure to the scheme of separation, that no one need be deceived.

The surface finish of the scientific stones is rarely as good as that of the natural material and it appears to be more difficult to produce a good polish on scientific stones than on natural ones. The degree of hardness of the scientific stones seems to be slightly variable in different parts of the same piece so that the polishing material removes the surface material unequally, leaving minute streaky marks on the surfaces of the facets. Possibly this condition might be remedied by skillful treatment, but hardly at the price obtainable for the product, so that a close study of the surface finish will sometimes help in distinguishing between natural and artificial material. Any fine specimen of natural ruby or sapphire will have usually received very expert treatment and a splendid surface finish.

In conclusion, then, the points to be remembered in determining the origin of corundum gems are four in number.

1. Expect to find natural defects, such as "silk" or cloudy patches, or angular bubbles in all natural stones.

2. If bubbles are present in artificial material they will be round or rounding.

3. Artificial material will always have curving parallel striae within it.

4. The surface finish of artificial material is seldom or never equal to that of natural material.

It ought not to be necessary to add that material from either source may be cut to any shape, and that artificial rubies may be seen in most Oriental garb, hence all specimens should have applied to them the above tests regardless of the seeming antiquity of their cut or of their alleged pedigree.



LESSON XVI

HOW TO TEST AN "UNKNOWN" GEM

Having now considered separately the principal physical properties by means of which one can identify a precious stone, let us attempt to give as good an idea as the printed page can convey of how one should go about determining to what species a gem belongs.

SIGNS OF WEAR IN AN EMERALD. To make the matter more concrete, and therefore more interesting, let us consider a real case, the most recent problem, in fact, that the author has had to solve. A lady of some wealth had purchased, for a large sum, a green stone which purported to be an emerald. After a few years of wear as a ring stone she noticed one day that the stone had dulled around the edges of its table, and thinking that that ought not to be the case with a real emerald, she appealed to a dealer in diamonds to know if her stone was a real emerald. The diamond merchant told her frankly that, while he was competent in all matters pertaining to diamonds, he could not be sure of himself regarding colored stones, and advised the lady to see the author.

The matter being thus introduced, the lady was at once informed that even a real emerald might show signs of wear after a few years of the hard use that comes to a ring stone.

While emerald has, as we saw in the lesson on hardness, a degree of hardness rated as nearly 8 (7-1/2 in the table), it is nevertheless a rather brittle material and the long series of tiny blows that a ring stone is bound to meet with will cause minute yielding along the exposed edges and corners of the top facets. This being announced, the first step in the examination of the stone was to clean it and to give it a careful examination with a ten-power lens. (An aplanatic triplet will be found best for this purpose.)

COLOR. The color was, of course, the most obvious property, but, as has already been said, color is not to be relied upon in all cases. In this case the color was a good emerald green but a bit bluer than the finest grass green. A very fine Maine tourmaline might approach this stone in color, so it became necessary to consider this possibility. A glass imitation, too, might have a color equal or superior to this.

IMPERFECTIONS. While noting the color, the imperfections of the stone claimed attention. They consisted mainly of minute jagged cracks of the character peculiar to brittle materials such as both emerald and tourmaline. So far it will be noted either of the above minerals might have furnished the lady's gem. As glass can be artificially crackled to produce similar flaws the stone might have been only an imitation as far as anything yet learned about it goes.

FILE TEST. The next step was to test its hardness by gently applying a very fine file to an exposed point at one corner of the girdle. The file slipped on the material as a skate slips on ice. Evidently we did not have to do with a glass imitation.

REFRACTION. Knowing now that we had a true hard mineral, it remained to be determined what mineral it was. On holding the stone in direct sunlight and reflecting the light onto a white card it was seen at once that the material was doubly refracting, for a series of double images of the back facets appeared. These double images might have been produced by tourmaline as well as by emerald. (Not however by glass which is singly refracting.) If a direct reading refractometer had been available the matter could have been settled at once by reading the refractive indices of the material, for tourmaline and emerald have not only different refractive indices but have double refraction to different degrees. Such an instrument was not available at the time and will hardly be available to most of those who are studying this lesson, so we can go on with our account of the further testing of the green stone.

HARDNESS. A test upon the surface of a quartz crystal showed that the stone was harder than quartz (but so is tourmaline). A true topaz crystal was too hard for the ring stone, whose edge slipped over the smooth topaz surface. The green stone was therefore not a green corundum (Oriental emerald) as the latter has hardness 9 and scratches topaz.

With hardness evidently between 7 and 8 and with double refraction and with the kind of flaws peculiar to rather brittle minerals we had in all probability either a tourmaline or an emerald.

DICHROISM. The dichroscope (which might have been used much earlier in the test but was not at hand at the time) was next tried and the stone was seen to have marked dichroism—a bluish green and a yellowish green appearing in the two squares of the instrument when the stone was held in front of the opening and viewed against a strong light.

As either tourmaline or emerald might thus exhibit dichroism (the tourmaline more strongly, however, than the emerald) one more test was tried to finally decide the matter.

SPECIFIC GRAVITY. The stone was removed from its setting and two specific gravity determinations made by means of a specific gravity bottle and a fine chemical balance. The two results, which came closely alike, averaged 2.70 which agrees very nearly with emerald (2.74) and which is far removed from the specific gravity of tourmaline (3.10). The stone was now definitely known to be an emerald, as each of several tests agreed with the properties of emerald, namely:

Color—nearly grass green.

Imperfections—like those of emerald.

Hardness—7-1/2.

Refraction—double.

Dichroism—easily noted.

Specific gravity—2.70.

While one who was accustomed to deal in fine emeralds might not need to make as detailed an examination of the stone as has just been indicated above, yet for most of us who do not have many opportunities of studying valuable emeralds it is safer to make sure by complete tests.

One other concrete example of how to go about testing unknown stones must suffice to conclude this lesson, after which the student, who has mastered the separate lessons preceding this, should proceed to test as many "unknowns" as his time and industry permit in order to really make his own the matter of these lessons. It may be added here that the task of testing a stone is much more rapid than this laborious effort to teach others how to do it might indicate. To one skilled in these matters only a few seconds are required for the inspection of a stone with the lens, the dichroscope, or the refractometer, and hardness tests are swiftly made. A specific gravity test requires more time and should be resorted to only when there remains a reasonable doubt after other tests have been applied.

Now for our final example. A red stone, cut in the form of a pear-shaped brilliant, was submitted to the writer for determination. It had been acquired by an American gentleman in Japan from an East Indian who was in financial straits. Along with it, as security for a loan, the American obtained a number of smaller red stones, a bluish stone, and a larger red stone. The red stones were all supposed to be rubies. On examination of the larger red stone with a lens it was at once noted that the internal structure was that of scientific ruby.

TESTING OTHER STONES. Somewhat dashed by the announcement of this discovery the owner began to fear that all his gems were false. Examination of the small red stones showed abundance of "silk," a peculiar fibrous appearance within the stone caused by its internal structure. The fibers were straight and parallel, not curved and parallel as in synthetic ruby. Tiny bubbles of angular shape also indicated that the small stones were natural rubies. They exhibited dichroism and scratched topaz and it was therefore decided that they at least were genuine.

The pear-shaped brilliant which was first mentioned was of a peculiar, slightly yellowish, red color. It was very pellucid and free from any striae either of the straight or curved types. It had in fact no flaws except a rather large nick on one of the back surfaces near the girdle. This was not in evidence from the front of the stone and had evidently been left by the Oriental gem cutter to avoid loss in weight while cutting the stone.

The peculiar yellowish character of the red color led us to suspect ruby spinel. The stone was therefore inspected with the dichroscope and found to possess no dichroism. The sunlight-card test, too, showed that the stone was singly refracting.

A test of the hardness showed that the material barely scratched topaz, but was attacked by sapphire. It was therefore judged to be a red spinel.

The large bluish stone which the gentleman acquired with the red stones proved to be iolite, sometimes called cordierite or water-sapphire (Saphir d'eau), a stone seldom seen in this country. It had marked dichroism—showing a smoky blue color in one direction and a yellowish white in another. The difference was so marked as to be easily seen without the dichroscope.



LESSON XVII

SUITABILITY OF STONES FOR VARIOUS TYPES OF JEWELS, AS DETERMINED BY HARDNESS, BRITTLENESS, AND CLEAVABILITY

HARD STONES NOT NECESSARILY TOUGH. As was suggested in the lesson on hardness there is prevalent in the public mind an erroneous belief that hardness carries with it ability to resist blows as well as abrasion. Now that it does not follow that because a precious stone is very hard, it will wear well, should be made plain. Some rather hard minerals are seldom or never used as gems, in spite of considerable beauty and hardness, because of their great brittleness. Other stones, while fairly hard and reasonably tough in certain directions, have nevertheless so pronounced a cleavage that they do not wear well if cut, and are sometimes very difficult to cut at all.

In view of these facts it will be well to consider briefly what stones, among those most in use, are sufficiently tough as well as hard, to give good service in jewels, such as rings, which are subject to rough wear. We may also consider those stones, whose softness, or brittleness, or ready cleavability, requires that they should be reserved for use only in those jewels which, because of their nature, receive less rough usage.

In order to deal with the principal gems systematically, let us consider them in the order of their hardness, beginning with the hardest gem material known, which is, of course, diamond.

DURABILITY OF THE DIAMOND. Fortunately this king of gems possesses in addition to its great hardness, considerable toughness, and although it is readily cleavable in certain directions it nevertheless requires a notable amount of force applied in a particular direction to cause it to cleave. Although sharp knocks will occasionally flake off thin layers from diamonds when roughly worn in rings, or even in extreme cases fracture them, yet this happens but seldom and, as the enormous use of the diamond in ring mountings proves, it is entirely suitable for that purpose. It follows that, if a stone can stand ring usage, it can safely be used for any purpose for which precious stones are mounted.

THE CORUNDUM GEMS. Next after the diamond in hardness come the corundum gems, i. e., ruby, sapphire, and the series of corundum gems of colors other than red and blue. These stones have no noticeable cleavage and are exceedingly tough, for minerals, as well as very hard. We have only to consider the use of impure corundum (emery) as a commercial abrasive in emery wheels, emery cloth, emery paper, etc., to see that the material is tough. Any of the corundum gems therefore may be used in any type of jewel without undue risk of wear or breakage. Customers of jewelers should, however, be cautioned against wearing ruby or sapphire rings on the same finger with a diamond ring in cases where it would be possible for the two stones to rub against each other. So much harder than the ruby is the diamond (in spite of the seeming closeness of position in Mohs's scale) that the slightest touch upon a ruby surface with a diamond will produce a pronounced scratch. The possessor of diamonds and other stones should also be cautioned against keeping them loose in the same jewel case or other container, as the shaking together may result in the scratching of the softer materials. The Arabs are said to have a legend to the effect that the diamond is an angry stone and that it should not be allowed to associate with other stones lest it scratch them.

CHRYSOBERYL. Passing on to the next mineral in the scale of hardness we come to chrysoberyl, which is rated as 8-1/2 on Mohs's scale. This mineral furnishes us the gem, alexandrite, which is notable for its power to change in color from green in daylight to red in artificial light. Chrysoberyl also supplies the finest cat's-eyes (when the material is of a sufficiently fibrous or tubular structure), and it further supplies the greenish-yellow stones frequently (though incorrectly) called "chrysolite" by jewelers. The material is very hard and reasonably tough and may be used in almost any suitable mounting.

SPINEL. After chrysoberyl come the materials rated as about 8 in hardness. First and hardest of these is spinel, then comes true or precious topaz. The various spinels are very hard and tough stones. The rough material persists in turbulent mountain streams where weaker minerals are ground to powder, and when cut and polished, spinel will wear well in any jewel. The author has long worn a ruby spinel in a ring on the right hand and has done many things that have subjected it to hard knocks, yet it is still intact, except for a spot that accidentally came in contact with a fast-flying carborundum wheel, which of course abraded the spinel.

TOPAZ. The true topaz is a bit softer than spinel, and the rough crystals show a very perfect basal cleavage. That is, they will cleave in a plane parallel to the bases of the usual orthorhombic crystals. This being the case a cut topaz is very likely to be damaged by a blow or even by being dropped on a hard surface, and it would be wiser not to set such a stone in a ring unless it was to be but little used, or used by one who would not engage in rough work while wearing it. Thus a lady might wear a topaz ring on dress occasions for a long time without damaging it, but it would not do for a machinist to wear one in a ring.

GEMS BETWEEN 7 AND 8 IN HARDNESS. We now come to a rather long list of gem minerals ranging between 7 and 8 in hardness. Of these the principal ones are zircon, almandine garnet, and beryl (emerald and aquamarine) rated as 7-1/2 in hardness, and pyrope and hessonite garnet rated as 7-1/4 in hardness. Tourmaline and kunzite may also be included in this group as being on the average slightly above 7 in hardness.

The above minerals are all harder than quartz, and hence not subject to abrasion by the quartz dust which is everywhere present. In this respect they are suitable for fairly hard wear. The garnets are of sufficient toughness so that they may be freely used in rings—and the extensive use of thin slices of garnet to top doublets proves the suitability of the material for resisting wear. The zircon is rather more brittle and the artificially whitened zircons (known as jargoons) are especially subject to breakage when worn in rings. Fortunately jargoons are not commonly sold.

The beryl, whether emerald or aquamarine, is rather brittle. Emeralds are seldom found in river gravels. The material cannot persist in the mountain streams that bring down other and tougher minerals. The extreme beauty and value of the emerald has led to its use in the finest jewels, and the temptation is strong to set it in rings, especially in rings for ladies. If such rings are worn with the care that valuable jewels should receive they will probably last a long time without any more serious damage than the dulling of the sharp edges of the facets around the table. This slight damage can at any time be repaired by a light repolishing of the affected facets. If an emerald is already badly shattered, or as it is called "mossy" in character, it will not be wise to set it in a ring, as a slight shock might complete its fracture. What has been said about emerald applies equally to aquamarine except that the value at stake is much less and the material is usually much freer from cracks.

Tourmalines, like emeralds, are brittle, and should be treated accordingly. Here, however, we are dealing with a much less expensive material than emerald, and if a customer desires a tourmaline in a ring mounting, while it will be best to suggest care in wearing it, the loss, in case of breakage, will usually be slight.

Kunzite, like all spodumene, has a pronounced cleavage. It should therefore be used in brooches, pendants, and such jewels, rather than in rings. Lapidaries dislike to cut it under some conditions because of its fragility.

QUARTZ GEMS. Coming down to hardness 7 we have the various quartz gems and jade (variety jadeite). The principal quartz gems are, of course, amethyst and citrine quartz (the stone that is almost universally called topaz in the trade). As crystalline quartz is fairly tough and lacks any pronounced cleavage, and as it is as hard as anything it is likely to meet with in use, it is a durable stone in rings or in other mountings. In the course of time the sharp edges will wear dull from friction with objects carrying common dust, which is largely composed of powdered quartz itself, and which therefore gradually dulls a quartz gem. Old amethysts or "topazes" that have been long in use in rings show this dulling. There is, however, little danger of fracture with amethyst or "topaz" unless the blow is severe and then any stone might yield.

The many semi-precious stones which have a quartz basis (such as the varieties of waxy or cryptocrystalline chalcedony which is largely quartz in a very minutely crystalline condition) are often even tougher than the clear crystallized quartz. Carnelian, agate, quartz cat's-eye, jasper (containing earthy impurities), and those materials in which quartz has more or less completely replaced other substances, such as silicified crocidolite, petrified wood, chrysocolla quartz, etc., are all nearly as hard and quite as tough as quartz itself, and they make admirable stones for inexpensive rings of the arts and crafts type.

JADE. Jade, of the jadeite variety, which is rarer than the nephrite jade, and more highly regarded by the Chinese, is an exceedingly tough material. One can beat a chunk of the rough material with a hammer without making much impression upon it. It is also fairly hard, about as hard as quartz, and with the two properties of toughness and hardness it possesses excellent wearing qualities in any kind of mounting. True jade, whether jadeite or nephrite, deserves a larger use in inexpensive ornaments, as it may be had of very fine green color and it is inexpensive and durable.

SOFTER STONES. Coming next to those minerals whose hardness is 6 or over, but less than 7, we have to consider jade of the nephrite variety, demantoid garnet ("olivine" of the trade), peridot (or chrysolite, or the olivine of the mineralogist), turquoise, moonstone, and opal.

As has already been said of jadeite, the jade of the nephrite variety, while slightly less hard, is about as tough a mineral as one could expect to find. It can take care of itself in any situation.

The demantoid garnet (the "olivine" of the trade) is so beautiful and brilliant a stone that it is a pity that it is so lacking in hardness. It will do very well for mounting in such jewels as scarf pins, lavallieres, etc., where but little hard wear is met with, but it cannot be recommended for hard ring use.

The peridot, too, is rather soft for ring use and will last much better in scarf pins or other mountings little subject to rubbing or to shocks.

Turquoise, although rather soft, is fairly tough, as its waxy luster might make one suppose, and in addition, being an opaque stone, slight dulling or scratching hardly lessens its beauty. It may therefore be used in ring mountings. However, it should be suggested that most turquoise is sufficiently porous to absorb grease, oil, or other liquids, and its color is frequently ruined thereby. Of course, such a change is far more likely to occur to a ring stone than to a turquoise mounted in some more protected situation.

The moonstone, being a variety of feldspar, has the pronounced cleavage of that mineral and will not stand blows without exhibiting this property. Moonstones are therefore better suited to the less rude service in brooch mountings, etc., than to that of ring stones. However, being comparatively inexpensive, many moonstones, especially of the choicer bluish type, are set in ring mountings. The lack of hardness may be expected to dull their surfaces in time even though no shock starts a cleavage.

THE OPAL. There remains the opal, of hardness 6, to be considered. As is well known opal is a solidified jelly of siliceous composition, containing also combined water. It is not only soft but very brittle and it will crack very easily. Many opals crack in the paper in which they are sold, perhaps because of unequal expansion or contraction, due to heat or cold. In spite of this fragility, thousands of fine opals, and a host of commoner ones, are set in rings, where many of them subsequently come to a violent end, and all, sooner or later, become dulled and require repolishing.

The great beauty of the opal, rivaling any mineral in its color-play, causes us to chance the risk of damage in order to mount it where its vivid hues may be advantageously viewed by the wearer as well as by others.

VERY SOFT STONES. Of stones softer than 6 we have but few and none of them is really fit for hard service. Lapis lazuli, 5-1/2 in hardness, has a beautiful blue color, frequently flecked with white or with bits of fool's gold. Its surface soon becomes dulled by hard wear.

Two more of the softer materials, malachite and azurite, remain to be described. These are both varieties of copper carbonate with combined water, the azurite having less water. Both take a good polish, but fail to retain it in use, being only of hardness 3-1/2 to 4.



LESSON XVIII

MINERAL SPECIES TO WHICH THE VARIOUS GEMS BELONG AND THE CHEMICAL COMPOSITION THEREOF

Although we have a very large number of different kinds of precious and semi-precious stones, to judge by the long list of names to be found in books on gems, yet all these stones can be rather simply classified on the basis of their chemical composition, into one or another of a comparatively small number of mineral species. While jewelers seldom make use of a knowledge of the chemistry of the precious stones in identifying them, nevertheless such a knowledge is useful, both by way of information, and because it leads to a better and clearer understanding of the many similarities among stones whose color might lead one to regard them as dissimilar.

MINERAL SPECIES. We must first consider what is meant by a "mineral species" and find out what relation exists between that subject and chemical composition. Now by a "mineral species" is understood a single substance, having (except for mechanically admixed impurities) practically a constant chemical composition, and having practically identical physical properties in all specimens of it.

DIAMOND AND CORUNDUM. A chemist would call a true mineral a pure substance, just as sugar and salt are pure substances to the chemist. Thus diamond is a "mineral species," as is also corundum. There are many different colors of both diamond and corundum, but these different colors are believed to be due to the presence in the pure substance of impurities in small amounts. Thus every diamond consists mainly of pure carbon, and all the corundum gems (ruby and the various colors of sapphire) consist mainly of pure oxide of aluminum. The properties of all diamonds are practically alike and so are the properties of all the corundum gems whether red (ruby), blue (sapphire), yellow (Oriental topaz), green (Oriental emerald), or purple (Oriental amethyst).

Thus all diamonds, of whatever color, belong to the one species, diamond, and in this case the usual custom in naming them agrees with the facts. Similarly all sapphires, of whatever color, belong to the mineral species "corundum." Thus a ruby is a red corundum.

The old French traveler and gem merchant, Tavernier, tells us that in the seventeenth century, when he visited the mines of Pegu, the natives knew of the similarity of the corundum gems and even called all by one name, with other names attached to designate the color. Singularly enough, the common name used by them was ruby rather than sapphire, as now. Thus they called blue corundum gems blue rubies; yellow corundums, yellow rubies, etc.

It is easily seen that if one recognizes the similar nature of all the many colors and shades of corundum that the number of things that one has to remember in order to be well acquainted with these stones is considerably diminished. Thus, instead of having a whole series of specific gravities to remember one has only to remember that all the corundum gems have a specific gravity of approximately 4. Similarly they are all of practically the same refractive index (1.761-1.770, being doubly refracting) that they all exhibit dichroism when at all deeply colored, etc.

Having thus indicated what we mean by mineral species and having illustrated the matter by the cases of diamond and corundum and further having stated that all diamonds are composed of pure carbon (except for traces of impurities) and all corundum gems mainly of oxide of aluminum, we may proceed to consider other mineral species and find out what gems they afford us.

CARBON, THE ONLY ELEMENT FURNISHING A GEM. It will be noted that the first species considered, diamond, consisted of but a single element, carbon. It is thus exceedingly simple in composition, being not only a pure substance but, in addition, an elementary substance. CORUNDUM, the second species considered, was a little more complex, having two elements, aluminum and oxygen, in its make-up, but completely and definitely combined in a new compound that resembles neither aluminum nor oxygen. It is thus a compound substance. No other element than carbon affords any gem-stone when by itself.

OXIDES OF METALS. There is, however, another oxide, in addition to aluminum oxide, that furnishes gem material. It is silicon oxide, containing the two elements silicon and oxygen. Silicon itself is a dark, gray, crystalline element that seems half metallic, half non-metallic in its properties. It is never found by itself in nature but about twenty-eight per cent. of the crust of the earth is composed of it in compound forms, and one of the most abundant of these is QUARTZ, which is a mineral species, and which contains just silicon and oxygen. That is, it is oxide of silicon. Now quartz is colorless when pure (rock crystal), but it is frequently found colored purple (probably by oxide of manganese) and it is then called amethyst by the jeweler. At other times its color is yellow (due to oxide of iron) and then the jeweler is prone to call it "topaz," although properly speaking that name should, as we shall soon see, be reserved for an entirely different mineral species. Chalcedony too (which when banded furnishes us our agates, and when reddish our carnelian) is a variety of quartz, and prase is only quartz colored green by fibers of actinolite within it.

The common cat's-eye and the tiger's-eye are varieties of quartz enclosing fibrous minerals or replacing them while still keeping the arrangement that they had. "Venus hair stone" is quartz containing needle-like crystals of rutile, and "iris" is quartz that has been crackled within, so as to produce rainbow colors, because of the effects of thin layers of material. Aventurine quartz (sometimes called goldstone) has spangles of mica or of some other mineral enclosed in it. The jaspers are mainly quartz with more of earthy impurity than the preceding stones.

Thus all this long list of stones of differing names can be classified under the one mineral species, quartz. Together they constitute the quartz gems. In properties they are essentially alike, having specific gravity 2.66, hardness 7, slight double refraction, etc., the slight differences that exist being due only to the presence of varying amounts of foreign matter.

OPAL. The opal may be considered along with the quartz gems, because, like them, it is composed mainly of oxide of silicon, but the opal also has water combined with the silicon oxide (not merely imprisoned in it). Thus opal is a hydrous form of silica (hydrous comes from the Greek word for water).

SPINEL. All our other stones are of more complicated chemical composition than the preceding. Coming now to mineral species which have three chemical elements in them we may consider first spinel, which has the two metallic elements aluminum and magnesium and the non-metallic element oxygen in it. It is virtually a compound of the two oxides, aluminum oxide and magnesium oxide. The variously colored spinels, like the various corundums, all have the same properties, thus they are all of hardness 8 or a little higher, they all have single refraction, and all have specific gravity 3.60.

CHRYSOBERYL. Another mineral species which, like spinel, has just three elements in its composition is chrysoberyl. This mineral contains the metals aluminum and beryllium combined with the non-metal oxygen. Thus it is really to be regarded as a compound of the two oxides, aluminum oxide and beryllium oxide. This species furnishes us Alexandrite, chrysoberyl cat's-eye and less valuable chrysoberyls of yellowish-green color. All are of the one species, the marked color difference being due to the presence of different impurities. The cat's-eye effect in one of the varieties is due to the internal structure rather than to the nature of the material.

THE SILICATES. Nearly all of the remaining precious stones belong to a great group of mineral species known as the silicates. These are so called because they consist largely of oxide of silicon (the material above referred to under quartz gems). This oxide of silicon is not free and separate in the silicates but is combined chemically with other oxides, chiefly with metallic oxides. Thus there are many different silicates because, in the earth, many different metallic oxides have combined with silicon oxide. Also in many cases two or three or even more metallic oxides have combined with silicon oxide to make single new compounds.

GLASS, A MIXTURE OF SILICATES. Those who are familiar with glass making may receive some help at this point by remembering that the various glasses are silicates, for they are made by melting sand (which is nearly pure oxide of silicon) with various metallic oxides. With lime (calcium oxide) and soda (which yields sodium oxide) we get soda-lime glass (common window glass). Lead oxide being added to the mixture a dense, very brilliant, but soft glass (flint glass) results. Cut glass dishes and "paste" gems are made of this flint glass. Now the glasses, although they are silicates, are not crystalline, but rather they are amorphous, that is, without any definite structure. Nature's silicates, on the other hand, are usually crystallized or at least crystalline in structure. (In a few cases we find true glasses, volcanic glass, or obsidian, for example.)

Having thus introduced the silicates we may now consider which ones among the many mineral silicates furnish us with precious or semi-precious stones.

BERYL, EMERALD, AND AQUAMARINE. First in value among the silicates is beryl, which, when grass green, we call emerald. The aquamarine and golden beryl too belong to this same species. Beryl is a silicate of aluminum and beryllium. That is, it is a compound in which oxide of silicon is united with the oxides of aluminum and of beryllium. There are thus four chemical elements combined in the one substance and it is hence more complicated in its composition than any of the gems that we have yet considered. It is worthy of note that aluminum occurs in the majority of precious stones, the only species so far considered that lack it being diamond, and the quartz gems.

Perhaps the silicates that are next in importance to the jeweler, after beryl, are those which form the garnets of various types. There are four principal varieties of garnet (although specimens of garnet frequently show a crossing or blending of the types).

GARNETS. The types are (1) Almandite garnet; (2) Pyrope garnet; (3) Hessonite garnet; and (4) Andradite garnet. These are all silicates, the almandite garnets being silicates of iron and aluminum; the pyrope garnets are silicates of magnesium and aluminum; the hessonite garnets, silicates of calcium and aluminum, and the andradite garnets, silicates of calcium and iron.

The so-called almandine garnets of the jeweler are frequently of the almandite class and tend to purplish red. The pyrope garnets are, as the name literally implies, of fire red color, as a rule, but they also may be purplish in color. The hessonite garnets are frequently brownish red and are sometimes called "cinnamon stones." The andradite garnets furnish the brilliant, nearly emerald green demantoids (so often called "olivine" by the trade).

Thus all the garnets are silicates and yet we have these four principal mineral species, which, however, are more closely related to each other in crystal form, in character of composition and in general properties, than is usual among the other silicates. Specimens which have any one of the four types of composition unblended with any of the other types would be found to be exactly alike in properties. As was suggested above, however, there is a great tendency to blend and this is well illustrated by the magnificent rhodolite garnets, of rhododendron hue which were found in Macon County, North Carolina. These had a composition between almandite and pyrope, that is, they had both magnesium and iron with aluminum and silica.

The true TOPAZ next calls for consideration as it too is a silicate. The metallic part consists of aluminum, and there are present also the non-metals fluorine and hydrogen. Here we have five elements in the one substance. Various specimens of this species may be wine yellow, light blue, or bluish green, pink or colorless, yet they all have essentially the same properties.

TOURMALINE is about as complicated a mineral as we have. It is a very complex silicate, containing aluminum, magnesium, sodium (or other alkali metal, as, for example, lithium), iron, boron, and hydrogen. As Ruskin says of it in his The Ethics of the Dust, when Mary asks "and what is it made of?" "A little of everything; there's always flint (silica) and clay (alumina) and magnesia in it and the black is iron, according to its fancy; and there's boracic acid, if you know what that is: and if you don't, I cannot tell you to-day and it doesn't signify; and there's potash and soda; and on the whole, the chemistry of it is more like a mediaeval doctor's prescription, than the making of a respectable mineral." The various tourmalines very closely resemble each other in their properties, the slight differences corresponding to differences in composition do not alter the general nature of the material.

MOONSTONE belongs to a species of mineral known as feldspar. The particular feldspar that furnishes most of the moonstone is orthoclase, a silicate of potassium and aluminum. Another feldspar sometimes seen as a semi-precious stone is Labradorite. Amazonite, also, is a feldspar. Sunstone is a feldspar which includes tiny flakes or spangles of some other mineral.

The mineral species olivine gives us peridot. It is a silicate of magnesium.

ZIRCON is itself a species of mineral and is a silicate of zirconium. The names hyacinth, jacinth, and jargoon are applied to red, yellow, and colorless zircon in the order as given.

JADE may be of any of several different species of minerals, all of which are very tough. The principal jades belong, however, to one or the other of two species, jadeite and nephrite. Jadeite is a sodium aluminum silicate and nephrite, a calcium magnesium silicate.

Leaving the silicates we find very few gem minerals remaining. The phosphates furnish us turquoise, a hydrous aluminum phosphate, with copper and iron. Variscite is also a phosphate (a hydrated aluminum phosphate).

The carbonates give us malachite and azurite, both carbonates of copper with combined water, the malachite having more water.



LESSON XIX

THE NAMING OF PRECIOUS STONES

Owing to the confusion which may result from a lack of uniformity in the naming of precious stones, it is very desirable that jewelers and stone merchants inform themselves in regard to the correct use of the names of the gems, and that they use care in speaking and in writing such names.

As nearly all precious and semi-precious stones are derived from a relatively small number of mineral species, as we saw in Lesson XVIII., and as the science of mineralogy has a very orderly and systematic method of naming the minerals, the best results are had in the naming of gems when we use, as far as is possible, the language of mineralogy.

ANCIENT USAGE. Long established custom and usage, however, must be observed, for any system of naming must be generally understood in order to be useful. Thus the proper name for blood red, crystallized oxide of aluminum, of gem quality, according to the mineralogical system of naming, would be red corundum, but that same material is referred to in the Old Testament thus (in speaking of wisdom), "She is more precious than rubies." It is obviously necessary to keep and to use all such terms as have been for years established in usage, even though they do not agree with the scientific method of naming the particular mineral. It is, however, necessary that any name, thus retained, should be correctly used, and that it should not be applied to more than one material. Thus the term ruby should be reserved exclusively for red corundum, and not applied to other red minerals such as garnet, spinel, etc., as is too often done.

It will be the purpose of this lesson to attempt to set forth as clearly and as briefly as possible what constitutes good usage in the naming of the principal stones, and also to point out what incorrect usage is most in need of being avoided.

To cover the subject systematically we will adopt the order of hardness that we did in discussing mineral species in Lesson XVIII.

FANCY DIAMONDS. Beginning with the hardest of all gems, the diamond, we have no difficulty as regards naming, as all specimens of this mineral, regardless of color, are called diamonds. When it is necessary to designate particular colors or tints, or differences in tint, additional names are used—for example, all diamonds of pronounced and pleasing color are called "fancy" diamonds in the trade. Certain of these "fancy" diamonds are still further defined by using a name specifying the color, as, for example, "canary" diamonds (when of a fine bright yellow), or "golden fancies," when of a fine golden brown, or "orange," or "pink," or "absinthe green," or "violet," as the case may be.

NAMES OF VARIOUS GRADES OF WHITE DIAMONDS. The great majority of the diamonds which come on the market as cut stones belong, however, to the group which would be spoken of as white diamonds, but many qualifying names are needed to express the degree of approach to pure white possessed by different grades of these diamonds. Thus the terms: 1, Jaegers; 2, Rivers; 3, Blue Wesseltons; 4, Wesseltons; 5, Top Crystals; 6, Crystals; 7, very light brown; 8, Top Silver Capes; 9, Silver Capes; 10, Capes; 11, Yellows, and 12, Browns, describe increasing depth of color, and hence decreasing value in diamonds.

POPULAR NAMES. Certain more popular names for diamonds of differing degrees of whiteness may next be set forth. The term "blue white" (a much abused expression, by the way) should be applied only to diamonds of such a close approach to pure whiteness of body substance, as seen on edge in the paper that, when faced up and undimmed, they give such a strong play of prismatic blue that any slight trace of yellow in their substance is completely disguised, and the effect upon the eye is notably blue. This would be the case with stones of the grades from 1 through 4 in the list above. Grades 5 and 6 might properly be called "fine white," and grades 7, 8, and 9 simply "white." Grade 10 is frequently spoken of as "commercial white," and grade 11 sometimes as "off color." Grade 12 includes all degrees of brownness except the very light shades and the deep, pretty shades of the "fancy" browns.

RUBIES. Leaving the naming of the different colors of diamonds we come to the gems furnished us by the mineral known as corundum. As we have previously seen, this mineral occurs in many different colors and with wide differences of tint and shade in each of the principal colors. The best practice with regard to naming the corundum gems is to call the red material, when of a good, full red of pleasing shade, ruby. The finest shades of blood red are usually called "Burmah rubies" because more rubies of this quality are found in Burmah than anywhere else. Any ruby of the required shade would, however, be called a Burmah ruby in the trade regardless of its geographical origin. The most desirable tint among Burmah rubies is that which is known as "pigeon blood" in color. This color is perhaps more accurately defined as like the color in the center of the red of the solar spectrum. Certain slightly deeper red rubies are said to be of "beef blood" color. The English are said to prefer these. Those of slightly lighter tint than pigeon blood are sometimes referred to as of "French color," from the fact that they are preferred by French connoisseurs.

Rubies of dark, garnet-like shade are known as "Siam rubies," many such being found in that country. Light pinkish rubies are called "Ceylon rubies." It should be clearly kept in mind that all these "rubies" are of red corundum, and that in all their distinctive properties except color they are essentially similar.

SAPPHIRES. Corundum of fine blue color is known as "sapphire." The "cornflower blue" seems to be most in favor at present. Such sapphires are sometimes called "Kashmir sapphires" because many fine ones come from that State. "Ceylon sapphires" are usually paler than the cornflower blue. "Montana sapphires" are usually of greenish blue or pale electric blue. Such fine blue stones as are mined in Montana would be sold under another name according to the quality of their color, and not as "Montana sapphires." "Australian sapphires" are of a very deep, inky blue, and do not command a high price. Here again, as with rubies, the classification depends upon the color rather than upon the origin, although the geographical names that are used, correctly state the usual source of stones of the particular color.

All corundums other than ruby and blue sapphire are usually called by the term "sapphire," with a qualifying adjective designating the color; thus we may have pink sapphire, golden sapphire, green sapphire, etc. When of very fine yellow color the yellow sapphire is sometimes called "Oriental topaz" by jewelers, the term "Oriental" as thus used indicating that the material is corundum. We also have "Oriental amethyst" and "Oriental emerald" for the purple, and the fine green, and "Oriental aquamarine" for the light blue-green corundum. The yellow corundum is also sometimes called "King topaz," especially in Ceylon. Inferior sapphires of almost every conceivable color are frequently assorted in lots and sold as "fancy sapphires." Such lots, however, almost always need reclassification as they often contain as many as a dozen mineral species besides corundum.

Sapphires and rubies of minute tubular internal structure frequently display a beautiful six-pointed star when cut to a round-topped cabochon shape and exposed to direct sunlight or to light from any other single source. Such stones are named "star sapphire" and "star ruby."

The artificial rubies and sapphires should all be called scientific ruby or sapphire, and not "reconstructed" or "synthetic" as none are made to-day from small, real rubies, and as the process is in no sense a chemical synthesis.

CHRYSOBERYL. Leaving the corundum gems we come next to chrysoberyl. When the gems furnished by this mineral are of a fine green by daylight, and of a raspberry red by artificial light, as is sometimes the case, they should be called "Alexandrites" (after the Czar Alexander II., in whose dominions, and on whose birthday, the first specimens are said to have been discovered). When chrysoberyl is of fibrous or tubular internal structure it affords cat's-eyes (when cabochon cut), and these should be specifically named as "chrysoberyl cat's-eye" to distinguish them from the less beautiful and less valuable quartz cat's-eyes. Other varieties of chrysoberyl (most of those marketed are of a greenish-yellow color) are correctly named simply "chrysoberyls." Such stones are, however, sometimes incorrectly called "chrysolite" by the trade, and this practice should be corrected, as the term chrysolite applies correctly only to the mineral olivine which gives us the peridot.

SPINEL. Next in the order that we have chosen comes "spinel." The more valuable spinels are of a red color that somewhat closely approaches the red of some rubies. Such red spinels should be called "Ruby spinel" (and not spinel ruby). The stones themselves sometimes get mixed with corundum rubies (they are frequently found in the same gem gravels), and this makes it all the more necessary that both stones and names should be clearly distinguished. Some dealers call reddish spinels "Balas ruby" (rose red), and orange red ones "rubicelle." Violet red spinel is sometimes called "almandine spinel." It is very desirable that the name of the mineral species, spinel, should be used, together with a qualifying color adjective, in naming gems of this species, rather than such terms as "rubicelle," "balas ruby," "spinel ruby," etc.

TOPAZ. We come now to topaz. True, or precious topaz, as it is usually called, to distinguish it from the softer and less valuable yellow quartz, is seldom seen in the trade to-day. Jewelers almost always mean yellow quartz when they speak of "topaz." This is an unfortunate confusion of terms, and one which will be hard to eradicate. There is seldom any injustice done through this misnaming, as the price charged is usually a fair one for the material offered. Considerably higher prices would be necessary if true topaz was in question.

An instance from the writer's experience will serve to illustrate the confusion that exists in the trade as to what should be called topaz. A jeweler of more than ordinary acquaintance with gems exhibited some fine brooch stones as specimens of topaz. On remarking that they were of course citrine quartz rather than true topaz, the author was met with the statement that the brooch stones were real topaz. In order to make clear to the dealer the difference between the two species, the author asked him if he hadn't some smaller topazes in stock that had cost him considerably more than the brooch stones. The dealer replied that he had some small wine yellow topazes for which he had paid more, and he produced them. The latter stones were true Brazilian topazes. Most of them had tiny, crackly flaws in them, as is frequently the case, and, as the writer pointed out to the dealer, they had been bought by the carat, whereas the large brooch stones had been bought at a certain price per pennyweight. In fact the little stones had cost more per carat than the larger ones had per pennyweight.

The dealer was then asked if there must not be some difference in the real nature of the two lots to justify paying more per carat for small, imperfect stones than per pennyweight for large perfect ones. He of course acknowledged that it would appear reasonable that such was the case. He was next shown that his small true topazes scratched his large stones easily, but the large ones could get no hold upon the surfaces of the small ones. (It will be remembered that topaz has a hardness of 8, while quartz has a hardness of 7.) The explanation then followed that the two lots were from two entirely distinct minerals, topaz and quartz, and that the former was harder, took a somewhat better polish, and was more rare (in fine colors) than quartz. Of course the yellow quartz should be sold under the proper name, citrine quartz. (From the same root that we have in "citrus" as applied to fruits. For example the "California Citrus Fruit Growers' Association," which sells oranges, lemons, grape fruit, etc. The color implication is obvious.) If the jeweler still wishes to use the term "topaz" because of the familiarity of the public with that name, then he should at least qualify it in some way. One name that is current for that purpose is "Spanish topaz," another is "Quartz-topaz." Perhaps the latter is the least objectionable of the names that include the word topaz.

Some of the wine yellow true topazes lose the yellow, but retain the pink component, on being gently heated. The resulting pink stone is rather pretty and usually commands a higher price than the yellow topazes. Such artificially altered topazes should be sold only for what they are, and probably the name "pinked topaz," implying, as it does, that something has been done to the stone, is as good a name as any. There is, however, little chance of fraud in this connection, as natural pink topazes are not seen in the trade, being very rare.

Some bluish-green topaz is said to be sold as aquamarine, and this confusion of species and of names should, of course, be stopped by an actual determination of the material as to its properties. Lacking a refractometer, the widely differing specific gravities of the two minerals would easily serve to distinguish them.



LESSON XX

THE NAMING OF PRECIOUS STONES (Concluded)

BERYL, EMERALD, AQUAMARINE. Coming now to beryl we have first emerald, then aquamarine, then beryls of other colors to consider. There is too often a tendency among dealers to confuse various green stones, and even doublets, under the name emerald. While the price charged usually bears a fair relation to the value of the material furnished, it would be better to offer tourmaline, or peridot (the mineral name of which is olivine), or demantoid garnet (sometimes wrongly called "Olivine"), or "emerald doublets," or emerald or "imitation emerald," as the case might be, under their own names.

There are no true "synthetic" or "scientific" or "reconstructed" emeralds, and none of these terms should be used by the trade. There has been an effort made in some cases to do business upon the good reputation of the scientific rubies and sapphires, but the products offered, when not out and out glass imitations, have usually been doublets or triplets, consisting partly of some pale, inexpensive, natural mineral, such as quartz or beryl, and a layer of deep green glass to give the whole a proper color. All attempts to melt real emerald or beryl have yielded only a beryl glass, softer and lighter than true emerald, and not crystalline, but rather glassy in structure. Hence the names "reconstructed," "synthetic" and "scientific" should never be applied to emerald.

The light green and blue green beryls are correctly called aquamarines, the pale sky-blue beryls should be named simply blue beryl. Yellow beryl may be called golden beryl, or it may be called "heliodor," a name that was devised for the fine yellow beryl of Madagascar. Beautiful pink beryl from Madagascar has been called "morganite," a name that deserves to live in order to commemorate the great interest taken by J. Pierpont Morgan in collecting and conserving for future generations many of the gems in the American Museum of Natural History in New York.

ZIRCON. We now come to a number of minerals slightly less hard than beryl, but harder than quartz, and zircon is perhaps as hard as any of these, so it will be considered next. Red zircon, which is rare, is properly called "hyacinth." Many Hessonite garnets (cinnamon stones) are incorrectly called hyacinths, however. The true hyacinth has more snap and fire owing to its adamantine surface luster and high dispersive power, as well as to its high refractive index. A true hyacinth is a beautiful stone. Golden yellow zircons are correctly called "jacinths." Artificially whitened zircons (the color of which has been removed by heating) are known as "jargoons" or sometimes as "Matura diamonds." All other colors in zircon should be named simply zircon, with a color adjective to indicate the particular color as, "brown zircon," etc.

TOURMALINE. Tourmaline furnishes gems of many different colors. These are all usually called simply tourmaline, with a color adjective to specify the particular color, as, for example, the "pink tourmaline" of California. Red tourmaline is, however, sometimes called "rubellite," and white tourmaline has been called "achroite." The latter material is seldom cut, and hence the name is seldom seen or used.

GARNET. We may next consider the garnets, as most of them are somewhat harder than quartz. As was said in Lesson XVIII. in our study of mineral species, there are several types of garnets, characterized by similarity of chemical composition, or at least by analogy of composition, but, having specific differences of property. The names used by jewelers for the several types of garnets ought to be a fairly true indication as to the type in hand in a particular case. At present there is considerable confusion in the naming of garnets. The most common practice is to call all garnets of a purplish-red color "almandines." As many such garnets belong to the mineral species almandite garnet, there is little objection to the continuance of this practice. The somewhat less dense, and less hard blood red garnets are properly called "pyrope garnets" (literally "fire" garnets). Many of the Arizona garnets belong in this division. The term "Arizona rubies" should not be used. As was said under ruby, nothing but red corundum should receive that title. Similarly the pyrope garnet of the diamond mines of South Africa is incorrectly called "Cape ruby." Pyrope and almandite garnet tend to merge in composition and in properties, and the beautiful "Rhodolite" garnets of Macon County, North Carolina, are between the two varieties in composition, in color, and in other properties.

Hessonite garnet furnishes yellowish-red and brownish-red stones, which are sometimes also called "cinnamon stones." They are also frequently and incorrectly called jacinth or hyacinth, terms which, as we have seen, should be reserved for yellow and red zircon, respectively.

Andradite garnet furnishes brilliant green stones, which have been incorrectly named "Olivines" by the trade. The name is unfortunate as it is identical with the true name of the mineral which gives us peridot. The name does not even suggest the color of these garnets correctly, as they are seldom olive green in shade. As the scarcity of fine specimens and their great beauty make a fairly high price necessary, the public would hardly pay it for anything that was called "garnet," as garnets are regarded as common and cheap. Perhaps the adoption of the name "Demantoid" might relieve the situation. The stones are frequently referred to as "demantoid garnets" on account of their diamond-like luster and dispersion. The use of "demantoid" alone, if a noun may be made from the adjective, would avoid both the confusion with the mineral olivine, and the cheapening effect of the word garnet, and would at the same time suggest some of the most striking properties of the material.

"Spodumene" furnishes pink to lilac "Kunzite," named after Dr. George F. Kunz, the gem expert, and for a time an emerald green variety was had from North Carolina which became known as "Hiddenite," after its discoverer, W. E. Hidden. No confusion of naming seems to have arisen in regard to this mineral.

The next mineral in the scale of hardness is quartz. (Hardness 7.) When pure and colorless it should be called "rock crystal." Purple quartz is of course amethyst. Some dealers have adopted a bad practice of calling the fine deep purple amethyst "Oriental" amethyst, which should not be done, as the term "Oriental" has for a long time signified a corundum gem. As Siberia has produced some very fine amethysts, the term "Siberian amethyst" would be a good one to designate any especially fine gem.

QUARTZ GEMS. We have already considered the naming of yellow quartz in connection with topaz. "Citrine quartz" is probably the best name for this material. If it is felt that the name "topaz" must be used, the prefix "quartz" should be used, or perhaps "Spanish topaz" will do, but some effort should be made to distinguish it from the true precious topaz. In addition to amethyst and citrine quartz we have the pinkish, milky quartz known as "rose quartz." This is usually correctly named.

"Cat's-eye" is a term that should be reserved for the Chrysoberyl variety, and the quartz variety should always be called "quartz cat's-eye." "Tiger's-eye" is a mineral in which a soft fibrous material has been dissolved away, and quartz has been deposited in its place. "Aventurine quartz" is the correct name for quartz containing spangles of mica. Clear, colorless pebbles of quartz are sometimes cut for tourists. Such pebbles are frequently misnamed "diamonds" with some prefix, as for example "Lake George diamonds," etc. Among the minutely crystalline varieties of quartz we have the clear red, which should be called "carnelian," the brownish-red "sard," the green "chrysoprase," the leek green "prase," and the brighter green "plasma." The last three are not so commonly seen as the first two, and frequently the best-colored specimens are artificially dyed.

"Jasper," a material more highly regarded by the ancients than at present, is mainly quartz, but contains enough earthy material to make it opaque. "Bloodstone" is a greenish chalcedony with spots of red jasper.

"Agates" are banded chalcedonies, the variety called "onyx" having very regular bands, and the "sardonyx" being an onyx agate in which some of the bands are of reddish sard.

Just as we considered opal with quartz (because of its chemical similarity) when discussing mineral species, so we may now consider the proper naming of opals here. "Precious opal" is distinguished from "common opal" by the beauty of its display rather than by any difference in composition. The effect is of course due to the existence of thin films (probably of material of slightly different density), filling what once were cracks in the mass. The rainbow colors are the result of interference of light (see a college text on physics for an explanation of interference). The varying thickness of these films gives varying colors, so different specimens of opal show very different effects. The differences of distribution of the films within the material also cause variations in the effects. Hence we have hardly any two specimens of opal that are alike.

There are, however, certain fairly definite types of opal and jewelers should learn to apply correct names to these types. Most prominent among the opals of to-day are the so-called "Black opals" from New South Wales. These give vivid flashes of color out of seeming darkness. In some positions the stones, as the name implies, appear blue-black or blackish gray. By transmitted light, however, the bluish stones appear yellow. Owing to the sharp contrast between the dark background and the flashing spectrum colors, black opals are most attractive stones and fine specimens command high prices. One fine piece, which was on exhibition at the Panama-Pacific Exposition was in the shape of an elongated shield, about 1-3/4 inches by 1-1/8 inches in size and rather flat and thin for its spread. It gave in one position a solid surface of almost pure ruby red which changed to green on tipping the stone to the opposite direction; $2,000 was asked for the piece.

"White opal" is the name applied to the lighter shades of opal which do not show the bluish-black effect in any position. "Harlequin opal" has rather large areas of definite colors giving somewhat the effect of a map of the United States in which the different States are in different colors.

"Fire opal" is an orange-red variety. It has some "play" of colors in addition to its orange-red body color.

"Opal Matrix" has tiny specks and films of precious opal distributed through a dark volcanic rock and the mass is shaped and polished as a whole.

JADE. "Jade" should next receive attention. It is a much abused term. Under it one may purchase jadeite, nephrite, bowenite, amazonite, or frequently simply green glass. The use of the word ought to be confined to the first two minerals mentioned, namely, jadeite and nephrite, for they only possess the extreme toughness together with considerable hardness that we expect of jade. Bowenite, while tough, is relatively soft and amazonite is brittle and also easily cleavable, while glass is both soft and brittle.

PERIDOT AND OLIVINE. The mineral "olivine" gives us the "peridot" (this name should be kept for the deeper bottle green stones), and the olive green gems of this same mineral may correctly be called "olivine" or "chrysolite." As was explained under garnet, jewelers frequently use the term "olivine" to designate demantoid garnet. The term chrysolite is also sometimes incorrectly used for the greenish-yellow chrysoberyl.

FELDSPAR GEMS. Among the minerals softer than quartz, which are used as gems, we have also "feldspar," which gives us "moonstone," "Labradorite," and "Amazonite."

An opalescent form of chalcedony is frequently gathered on California beaches and polished for tourists under the name of "California Moonstone." This name is unfortunately chosen as the material is not the same as that of true moonstone and the effect is not so pronounced or so beautiful. The polished stones show merely a milky cloudiness without any of that beautiful sheen of the true moonstone. "Labradorite" is usually correctly named. "Amazonite" was originally misnamed, as none is found along the river of that name. The term has come into such general use, however, that we shall probably have to continue to use it, especially as no other name has come into use for this bluish-green feldspar. As has already been said, amazonite is sometimes sold as "jade," which is incorrect.

MALACHITE, AZURITE, AND LAPIS LAZULI. Malachite and azurite are usually correctly named, but "lapis lazuli" is a name that is frequently misused, being applied to crackled quartz that has been stained with Prussian blue, or some other dye, to an unconvincing resemblance to true lapis. Such artificially produced stones are sometimes sold as "Swiss lapis." They are harder than true lapis and probably wear much better in exposed ornaments, but they are not lapis and are never of equal color, and names should not be misused, and especially is this true in a trade where the public has had to rely so completely upon the knowledge and the integrity of the dealer.

With the increase of knowledge about precious stones that is slowly but steadily growing among the public, it becomes more than ever necessary for the jeweler and gem dealer to know and to use the correct names for all precious stones. The student who wishes to learn more about the matter will have to cull his information from many different works on gems. G. F. Herbert-Smith, in his Gem-Stones, gives a three and one half page chapter on "Nomenclature of Precious Stones" (Chap. XIII., pp. 109-112). The present lesson has attempted to bring together in one place material from many sources, together with some suggestions from the author.



LESSON XXI

WHERE PRECIOUS STONES ARE FOUND

OCCURRENCE OF DIAMOND. Every dealer in precious stones should know something of the sources of the gems that he sells. The manner of the occurrence of the rough material is also a matter of interest. It will therefore be the purpose of this lesson to give a brief account of the geographical sources of the principal gems and of their mode of occurrence in the earth.

For the sake of uniformity of treatment we will once more follow the descending order of hardness among the gems and we thus begin by describing the occurrence of diamond. It will be of interest to note first that the earliest source of the diamond was India, and that for many years India was almost the sole source. Tavernier tells us that the diamond mining industry was in a thriving state during the years from 1640 to 1680, during which time he made six journeys to India to purchase gems. He speaks of Borneo as another source of diamonds, but most of the diamonds of that time were furnished by India.

"GOLCONDAS." Indian diamonds were noteworthy for their magnificent steely blue-white quality and their great hardness, and occasionally one comes on the market to-day with an authentic pedigree, tracing its origin back to the old Indian mines, and such stones usually command very high prices. One of a little over seven and one half carats in weight, in the form of a perfect drop brilliant, has lately been offered for sale at a price not far from $1,000 per carat. Such diamonds are sometimes called "Golcondas" because one of the mining districts from which the fine large Indian stones came was near the place of that name. Some of the stones from the Jaegersfontein mine in South Africa resemble the Golcondas in quality. Many of the large historical crown diamonds of Europe came from the Indian mines.

The stones were found in a sedimentary material, a sort of conglomerate, in which they, together with many other crystalline materials, had become imprisoned. Their original source has never been determined. They are therefore of the so-called "River" type of stone, having probably been transported from their original matrix, after the disintegration of the latter, to new places of deposit, by the carrying power of river waters.

The Indian mines now yield very few stones. The United States Consular reports occasionally mention the finding of a few scattered crystals but the rich deposits were apparently worked out during the seventeenth century and the early part of the eighteenth century.

In 1725 and in the few following years the Brazilian diamond fields began to supersede those of India. Like the latter, the Brazilian fields were alluvial, that is, the materials were deposited by river action after having been carried to some distance from their original sources.

BRAZILIAN DIAMONDS. The diamonds of Brazil also resembled those of India in quality, being on the average better than those of the present South African mines. It may be added that even the African diamonds that are found in "river diggings" average better in quality than those of the volcanic pipes which form the principal source of the world's supply to-day. There seems to be a superabundance of iron oxide in the rocks of the African mines and in the diamonds themselves, imparting yellow or brownish tints to the material. The "River" stones seem to have lost this color to a considerable extent, if they ever had it. Possibly long extraction with water has removed the very slightly soluble coloring material. Whatever the cause of their superiority "River" stones have always been more highly regarded than stones from the volcanic pipes.

Brazil furnished the world's principal supply of diamonds until the discovery of the African stones in 1867. At present relatively small numbers of Brazilian stones reach the world's markets. Most of these come from the great Bahia district (discovered in 1844) rather than from the older mines of Brazil. The present Brazilian stones average of small size. They are, however, of very good quality as a rule. A few green stones are found in Brazil and these may be of an absinthe-green or of a pistachio-green tint.

AUSTRALIAN AND AMERICAN SOURCES. While a few diamonds now come on the market from New South Wales, and while an occasional stone is found in the United States (usually in glacial drift in the north central States, or in volcanic material somewhat resembling that of South Africa in Arkansas) yet the world's output now comes almost entirely from South Africa and mainly from the enormous volcanic pipes of the Kimberly district and those of the Premier Co. in the Transvaal.

SOUTH AFRICAN DIAMONDS. The nature of the occurrence of diamond in the "pipes" of South Africa is so well known to all who deal in diamonds to-day that but little space need be devoted to it. The "blue ground," as the rock in which the diamonds are found is called, seems to have been forced up from below, perhaps as the material of a mud volcano, bringing with it the diamonds, garnets, zircons, and the fifty or more other minerals that have been found in the blue ground. The fragmentary character of some of these minerals would indicate that the blue ground was not their original matrix. How the diamonds originally crystallized and where, is still probably a matter for further speculation.