Project Gutenberg's A Hand-book of Precious Stones, by Meyer D. Rothschild This eBook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at www.gutenberg.org. If you are not located in the United States, you'll have to check the laws of the country where you are located before using this ebook. Title: A Hand-book of Precious Stones Author: Meyer D. Rothschild Release Date: October 17, 2019 [EBook #60512] Language: English Character set encoding: UTF-8 *** START OF THIS PROJECT GUTENBERG EBOOK A HAND-BOOK OF PRECIOUS STONES *** Produced by Paul Marshall and the Online Distributed Proofreading Team at http://www.pgdp.net (This file was produced from images generously made available by The Internet Archive) A HAND-BOOK OF PRECIOUS STONES BY M. D. ROTHSCHILD NEW YORK & LONDON G. P. PUTNAM’S SONS The Knickerbocker Press 1890 COPYRIGHT BY M. D. ROTHSCHILD 1889 The Knickerbocker Press, New York Electrotyped and Printed by G. P. Putnam’s Sons [Pg i] CONTENTS. PAGE What are Precious Stones? 7 Physical Characters— Crystallization 10 Cleavage 10 Fracture 11 Optical Properties— Refraction 12 Polarization of Light 13 Pleiochroism 14 Colors 15 Lustre 17 Streak 18 Hardness 19 Specific Gravity 21 Weight 27 Fusibility 28 Magnetism 30 Transparency 30 Phosphorescence 31 Electricity 31 Cutting and Polishing 32 Diamond 35 Corundum 39 The Ruby 40 Sapphire 43 Fancy Sapphires 44 Star Sapphires 45 Spinel 46 Beryl 50 Emerald 51 Beryl 53 Chrysoberyl 54 Cymophane 56 Alexandrite 56 Zircon 58 Turquois 60 Tourmaline 64 Opal 69 Pearl 71 Chrysolite 78 Garnet 80 Topaz 84 Apatite 87 Felspar 88 Moonstone 89 Sunstone (Avanturine Felspar) 90 Amazon Stone (Green Felspar) 91 Labradorite 91 Cyanite 93 Lapis Lazuli 94 Hiddenite 95 Spodumene 96 Dichroite 97 Idocrase 98 Euclase 99 Sphene 100 Phenacite 101 Epidote 101 Axinite 102 Diopside 103 [Pg ii] [Pg iii] Fluor Spar 104 Hypersthene 105 Quartz 106 Crystallized Quartz 109 Amethyst 110 Yellow Quartz 111 Cairngorm, etc 111 Rose Quartz 113 Avanturine 114 Cat’s-Eye 114 Crocidolite 115 Heliotrope 116 Chrysoprase 117 Prase 117 Plasma 118 Chalcedony 118 Agates 119 Onyx or Agate Onyx 120 Carnelian 122 Jasper 123 False Lapis 124 Hematite 124 Obsidian 125 Malachite 126 Jet 128 Amber 128 Coral 130 Table of Hardness and Specific Gravity 132 Index 135 [Pg iv] [Pg 5] PREFACE. The object of this little book is to convey to the merchant, the workman, and the amateur, in a condensed and accurate form, information concerning the various properties of precious stones. Besides drawing freely on a number of authorities, the author has used his practical experience to indicate such tests as an amateur can readily make. Specific gravity, hardness, and dichroism are tests which are easily mastered, and a thorough understanding of these three properties will assist in classifying doubtful gems. Such stones have been dealt with principally as are used in commerce for jewelry and ornamental purposes. The attention of the writer has often been called to the general lack of knowledge among the jewelers regarding precious stones other than diamonds, rubies, sapphires, and emeralds. As there are so many other beautiful and rare gems which nature yields to man, and which are worthy of the jewelers’ art, the author trusts that his book will awaken a new interest in the fascinating study of mineralogy as applied to precious stones, and that at some future day he may feel encouraged to enlarge upon this treatise. M. D. ROTHSCHILD. 41 and 43 Maiden Lane, New York. [Pg 6] HAND-BOOK OF PRECIOUS STONES. What are Precious Stones? The mineral to which the term “precious stone” is applied, must be adaptable for jewelry or ornamental purposes and must possess beauty, hardness, and rarity. The beauty of a precious stone or gem consists of its color or colorlessness, brilliancy or softness of lustre, and transparency. To take a high and lasting polish, a mineral must be hard,—and many stones that would otherwise be highly valued are low in the estimate of worth because they do not possess of sufficient hardness to make them endure the wear and friction to which a precious stone is subjected when used in the form of jewelry. The rareness of precious stones has a decided effect in determining their values. For instance, the crocidolite, commercially known as tiger-eye, was sold by the carat some years ago, and was largely used in the making of fine jewelry. To-day, this material is so plentiful that it is no longer classed among the higher gems, but serves for cameos and intaglios like chalcedony and onyx. The changes of fashion have much to do with determining the market value of precious stones. Amethysts, topazes, cat’s-eyes, aquamarines, alexandrites, and even emeralds and opals have been eagerly sought for at times and then again neglected for other gems, causing a sensible difference in the value of these stones. There are all degrees of precious stones, from the valuable diamond and corundums to the humbler quartz, amethyst, and topaz. It has been a mooted question as to the proper dividing line between stones that deserve the title “precious,” and those which should be placed in a so-called semi-precious or lower category. To draw such a line is hardly possible, as neither hardness, rareness, nor value would be a positive test—some of the hard stones, like zircon and almandines being less valuable than the softer opal, while the diamond, one of the most plentiful of precious stones, is at the same time, one of the most valuable. Neither can price be taken as a complete test, because fashion makes a turquois, an opal, or an emerald much more valuable at one time than at another. All precious minerals used for ornamental purposes, from the diamond to quartz, or chalcedony, may properly be termed precious stones. [Pg 7] [Pg 8] [Pg 9] [Pg 10] Physical Characters. CRYSTALLIZATION. Precious stones are found either in crystallized or amorphous conditions. The forms of crystallization are: 1 Isometric or Cubic; having the axes equal. 2 Tetragonal or Pyramidal having only the lateral axes equal. 3 Hexagonal or Rhombohedral 4 Orthorhombic or Trimetric having the axes unequal. 5 Monoclinic or Oblique 6 Triclinic or Anorthic Most precious stones crystallize, but the specimens that have the crystallization clearly defined are seldom found. The amorphous condition includes the turquois, opal, and obsidian, which minerals are found in masses or veins surrounded by a matrix. CLEAVAGE. Many minerals can be separated readily in one direction by simply making a small indentation with a harder mineral, then introducing the blade of a knife into the scratch and striking it a sharp blow,—this separates the crystal. There are certain planes at right angles where the crystal can be separated; this property is called cleavage and the planes, cleavage planes. In some minerals cleavage is difficult to produce, while in others such as mica and rock-salt, cleavage is highly perfect and the number of separations produced is only limited by the thickness of the blade used in separating the planes. The property of cleavage is very useful and of great assistance to the lapidary, as it enables him to shape a diamond or other hard stone nearly to the size he desires, and at the same time to save the extra material cleaved off, which can be used for smaller gems, and which under other conditions would have to be ground away. FRACTURE. Fracture surfaces are the result of the breaking of a crystal otherwise than by cleaving, and in a different direction from the cleavage planes. When the form of fracture is composed of concave and convex surfaces it is called conchoidal; when free from inequalities it is known as even or smooth, and when covered by small splinters, splintery or uneven. [Pg 11] [Pg 12] Optical Properties. REFRACTION. When a ray of light passes from one medium to another, or from the air to a crystal it is bent or refracted; this is called single refraction and takes place in the diamond, spinel, and garnet. Most of the other transparent precious stones possess double refraction—that is, the ray of light enters the crystal and divides into two parts, one following the ordinary laws of refraction, while the other part or extraordinary ray does not obey the usual law. There are precise methods for measuring the indices of refraction, but they are not applicable to polished gem stones. POLARIZATION OF LIGHT. Polarization is a peculiar modification which, under certain conditions, a ray of light undergoes. This property is easier to observe than double refraction. If from a transparent prism of tourmaline two thin plates are cut, parallel to its axis, they will transmit light when they are placed above each other with the chief axis of each in the same direction. When one of the plates is turned at right angles to the other, no light, or but very little, is transmitted, so that the plates appear black. In passing through the first slip, the rays of light have acquired a peculiar property, which renders them incapable of being transmitted through the second, except when the two are held in a parallel position, and the rays are then said to be polarized. In some doubly refracting crystals the two oppositely polarized beams are of different colors, so upon double refraction and polarization depends the property of many gems which is called pleiochroism. Pleiochroism. The dichroiscope is a handy little optical instrument, that will readily serve to distinguish the diamond, spinel, or garnet (all singly refracting minerals) from the ruby, beryl, or any of the doubly refracting stones. This instrument consists of a cleavage rhombohedron of Iceland spar, fastened in a brass tube about 2½ inches long, and ¾ of an inch in diameter. A sliding cap at one end has a perforation ⅛ of an inch square, and at the other end is a lens which will show a distinct image of the square opening when the cap is pulled out about ¼ of an inch. Dichroiscope Fig. 1. The pleiochroism of many stones can be determined at a glance with the dichroiscope. When a stone is examined by means of the dichroiscope, it will show two images of the same hue, or of different hues, these square images (fig. 1, A) forming a right angle and being more distinct when viewed from one part of the stone than from another. When the images are identical in color, the specimen may be a diamond, garnet, spinel, or glass. Should a red or ruby spinel approach the ruby in color, a quick and satisfactory test can be made with the dichroiscope, as the spinel will show two images of one color, while the ruby will show one image of aurora red and one of carmine red. The dichroiscope is inexpensive, costing but a few dollars, and is very useful for rapidly deciding the species of many stones. The following is a partial list of doubly refracting stones and their twin colors. NAME OF STONE. TWIN COLORS. Sapphire (blue) Greenish straw Blue Ruby (red) Aurora red Carmine red Tourmaline (red) Salmon Rose pink " (brownish red) Umber brown Columbine pink " (brown) Orange brown Greenish yellow " (green) Pistachio green Bluish green " (blue) Greenish gray Indigo blue Emerald (green) Yellowish green Bluish green Topaz (sherry) Straw yellow Rose pink Peridot (pistachio) Brown yellow Sea green Aquamarine (sea green) Straw white Gray blue [Pg 13] [Pg 14] [Pg 15] [Pg 16] Beryl (pale blue) Sea green Azure blue Chrysoberyl (yellow) Golden brown Greenish yellow Iolite (lavender) Pale buff Indigo blue Amethyst (purple) Reddish purple Bluish purple NAME OF STONE. TWIN COLORS. Colors. The following is a partial list of the colors of precious stones: Shades of White.—Quartz, opal, chalcedony. Shades of Gray.—Labrador, smoky topaz, chalcedony, zircon. Black.—Obsidian, tourmaline, jet. Shades of Blue.—Lapis-lazuli, amethyst, chalcedony, spinel, zircon, sapphire, cyanite, tourmaline, turquois, odontolite, fluor spar. Shades of Green.—Amazon stone, turquois, prase, beryl, blood-stone, epidote, emerald, malachite, chrysoprase, chrysolite, idocrase, olivine, garnet, chrysoberyl. Shades of Yellow.—Opal, amber, topaz, beryl, jasper. Shades of Red.—Garnet, carnelian, chalcedony, rose quartz, corundum, tourmaline, spinel, ruby. Shades of Brown.—Zircon, garnet, smoky topaz, axinite, jasper. Colorless.—Diamond, sapphire, spinel, zircon, topaz, rock crystal, moonstone. Lustre. Well polished precious stones display a decided lustre, which assists in determining their species. The following is a list of some precious stones and their lustre: Adamantine.—Diamond, zircon. Resinous.—Garnet. Vitreous.—Emerald, ruby, spinel. Waxy.—Turquois. Pearly.—Moonstone, opal. Silky.—Crocidolite, quartz cat’s-eye. Metallic.—Hematite. Greasy.—Olivine. Some stones vary in lustre, from vitreous to pearly, etc. Streak. The streak of a mineral is the color of its powder. This powder varies in color, and may be white, gray, red, etc. It is obtained by scratching the mineral with a sharp file, or by rubbing the mineral on the back of an unglazed porcelain plate, when the color of the powder will appear on the plate. It is remarkable that the streak of the diamond is gray to grayish-black, while that of the ruby is colorless or white. Hardness. One of the most important and distinguishing qualities of a gem stone is the property of enduring, resisting wear,—in short, hardness. To test the hardness of precious stones that have not been cut or polished, the following scale of ten minerals has been devised by Moh, a German mineralogist: No. 1. Talc. Very soft; is easily broken or scratched with the finger-nail. No. 2. Rock-salt. Soft; scratched with difficulty with finger-nail; readily cut with a knife. No. 3. Calcite. Low degree of hardness; not to be scratched with finger-nail; easily scratched with a knife. No. 4. Fluor spar. Fairly hard; is slightly scratched by a knife, but easily attacked with a file. No. 5. Apatite. Medium hardness; does not scratch glass, or only faintly; does not give out sparks against steel; easily attacked with a file. No. 6. Felspar. Easily scratches glass; is attacked by a file, and gives some sparks against steel. No. 7. Quartz. Quite hard; is only slightly attacked by file; gives sparks readily against steel. No. 8. Topaz. Very hard; is not attacked by a file. [Pg 17] [Pg 18] [Pg 19] [Pg 20] No. 9. Sapphire. Hardest of all minerals but the diamond; attacks all other minerals. No. 10. Diamond. Attacks all minerals; is not attacked by any. To find the hardness of a stone, begin to test with the softest mineral, so that when the number is reached which will scratch the stone, there has been no injury to the specimen under examination. Half numbers are determined by the ease or difficulty with which a stone is scratched. For example, a stone which will resist No. 7 (quartz) and which is only faintly attacked by No. 8 (topaz) may be safely put down as 7.5, while a stone which resisted No. 7 and yielded easily to No. 8 is to be classed as 7 in hardness. These tests are readily applied to crystals or unpolished gems. With the polished stone greater care must be observed, and while a file test is often satisfactory, there is always the danger of striking the cleavage and breaking off a small piece of the stone. Specific Gravity. One of the most important tests which can be applied to a polished stone is that of specific gravity. Many stones, like the ruby and the spinel, the blue tourmaline and the sapphire, etc., look alike, but there is a sensible difference in their respective weights that a specific-gravity test will readily establish. The weight of an object which is free to seek the centre of gravitation is called absolute weight, while the weight of an object compared with that of another containing the same volume of matter is called the specific weight. If a stone weighing 16 carats is placed in a vessel filled to the brim with distilled water and the stone displaces 6 carats of water, the specific gravity of the stone would be 16 ÷ 6, or 2.66, the specific gravity of quartz. In other words, the stone would weigh 16 carats in the air and only 10 carats in the distilled water, showing a loss of 6 carats, which is the weight of the volume of water equal in bulk to the stone;—or absolute weight, 16 carats; specific weight, 10 carats; loss, 6 carats; 16 ÷ 6 = 2.66, specific gravity. There are several methods of ascertaining the specific gravity of a stone. First, by placing it in liquids of known specific gravity. Second, by weighing the stone in air and then in distilled water or alcohol, and thus learning the weight of an equal bulk of water. Third, by measuring or weighing the water which the stone displaces when immersed in a small vessel of known capacity. Fourth, by means of the Nicholson hydrometer, a simple instrument consisting of a hollow glass cylinder, two dishes, and a glass vessel. As the jewelers’ balances are well adapted for the ordinary work of taking specific gravity, or can be easily adapted for such work, the second method will usually be the more practical to follow. The author has had very satisfactory service from a $30 balance, and any well adjusted balance will give fair results. The following accessories are necessary to take the specific gravity of a stone: Distilled water about 60° Fahr. A very fine thread of platinum wire with which to suspend the stone (fig. 4). A glass-beaker for the water (fig. 3, C). A bench to hold the beaker over the pan (fig. 2). FIG. 4. Platinum wire. FIG. 2. Bench. Test set-up. Fig. 3. The distilled water is easily obtainable from any druggist. The platinum wire should be bent to hook into the top of the balance frame, (fig. 3, B) and for ordinary small stones it will be convenient to twist the other end into a cork-screw shape or receptacle (fig. 4, A). The beaker can be a small, thin glass cup of any kind, and the bench is easily produced from wood (fig. 2) or of metal with three supports (fig. 3, A). [Pg 21] [Pg 22] [Pg 23] [Pg 24] [Pg 25] [Pg 26] To ascertain the specific gravity, attach the platinum wire to the balance frame, (fig. 3, B) and allow the lower end to rest in the water; then balance this carefully by adding weights to the other side (fig. 3, D) until the balance is exact. The stone to be weighed in water is a ruby, and weighs two carats in the air. Clean the stone carefully with water to free it from air bubbles; then place it in the screw of the wire (fig. 4, A) and weigh carefully. If the stone weighs 1½ carats it will have displaced ½ ct. of water: or, weight in air, 2 carats; weight in water, 1½ carats; loss, ½ carat; 2 ÷ ½ = 4, which will be the specific gravity of the ruby. The Jolly spiral balance can also be used for taking specific gravity, but it is not so practical or accurate for small stones as for the larger ones. Weight. The valuable precious stones are bought and sold by the carat. This weight is equal to about 3.17 grains or about .205 milligrams. The carat is divided into fractions of ½, ¼, ⅛, 1⁄16,1⁄32, 1⁄64, and also arbitrarily into four grains; that is, each quarter of a carat is counted one grain, thus forming the basis for the calculation of pearls. In commerce, a carat diamond is sometimes called a four-grain stone, and a carat-and-a-half stone is six grains, etc., etc. The weight of the carat being arbitrary, it varies in different countries, some being heavier and others lighter than .205 milligrams. The writer wrote to three prominent balance-makers in the United States some months ago for their carat standards and was surprised to find that they all differed. This will account for discrepancies in weight resulting between the balances of different makers. Of late there has been a decided movement in Europe, headed by the French Chambre Syndicale of jewelers, in favor of the unification of the carat, so that the weight of a French or Dutch carat will equal that of an English, American, or any other carat. This reform will probably be accompanied by the adoption of the decimal system of dividing the carat, and the discarding of the complicated fractional system. After having tried the decimal weights for many months, the author can testify to a decided gain in time and accuracy from their use. Fusibility. The blow-pipe or dry test for minerals is convenient to apply to small bits or splinters of a stone. The mineral is either held by a pair of platina-pointed forceps, or powdered and placed on a metal plate or in a glass tube. Before the blow-pipe, some minerals change color, but do not melt, while others retain their color, or swell up, or break into small particles, or melt into colorless or colored glasses. The following is the scale of minerals used to test the different degrees of fusibility: 1. Gray Antimony. Fusible in coarse splinters in summit of candle flame without the blow-pipe. 2. Natrolite. Fusible in fine splinters in the summit of a candle flame without the blow-pipe. 3. Almandite. Does not fuse in candle flame; fuses easily before the blow-pipe in obtuse pieces. 4. Green Actinolite. Fusible before the blow-pipe in coarse splinters. 5. Orthoclase. Fusible before the blow-pipe in fine splinters. 6. Bronzite. Before the blow-pipe becomes rounded only on the sharp edges. Magnetism. There are but few precious stones that possess the power to act on the magnetic needle; among them are the chrysolite, cinnamon stone, almandine, pyrope, and garnet. Transparency. Precious stones are, on the basis of their relative transparency, divided into four classes, as follows: Transparent, or admitting light freely and clearly; defining objects when used as a lens. Semi-transparent, admitting light, but only partially defining objects. Translucent, admitting light faintly. Opaque, not admitting light. The more valuable precious stones, excepting opals and turquoises, are generally transparent. Phosphorescence. [Pg 27] [Pg 28] [Pg 29] [Pg 30] [Pg 31] Some precious stones display a distinct phosphorescence after exposure to the sunlight, and also upon the application of artificial heat, and through mechanical and electrical means. Many diamonds, when taken to a dark room, appear quite luminous; this is also true of topaz, fluor spar, and other minerals. Electricity. Minerals acquire electricity through friction or heating, and in this state readily attract or repel small bits of paper and other light substances. All minerals are electric, some displaying positive and others negative electricity. The electric test of a precious stone refers to the length of time that a stone will retain electricity after friction or heating. Some stones lose this quality in a few minutes, while others retain it a long time. The tourmaline is noted for its electrical properties, while the Brazilian topaz rendered electric by heating or rubbing has been known to affect the electric needle after 32 hours. Cutting and Polishing. Although a finely developed diamond, ruby, or other crystal is sometimes found and used for jewelry, the beauty of a precious stone generally remains hidden within a rough and unsightly exterior until the lapidary’s art reveals the gem. According to well known rules, there is one kind of cutting or faceting for the diamond or colorless gems and another for colored gems. The brilliant cut, figs. 5 and 6, consists of an arrangement of fifty-six facets, exclusive of the table and culet. This cut is sometimes improved by the addition of eight star facets around the culet, which brings the number of facets up to sixty-four. The following are the proportions of a well cut diamond or colorless gem: ⅓ above the girdle, fig. 6, A. ⅔ below " " " 6, B. The table 2⁄5 of the breadth of the stone, fig. 6, C. The culet ⅙ of the size of the table, fig. 6, D. Fig. 5. Fig. 6. These proportions do not refer to colored gems, which are cut thick or shallow to deepen or diminish the color of the stone. The step cut, fig. 7, now principally used for emeralds, can be advantageously used for other colored stones. The crowned rose cut, fig. 8, is applied to small diamonds, and occasionally to colored gems. This cut consists of twenty-four facets, and a well proportioned rose is one half of its diameter in thickness. Fig. 7. Fig. 8. Fig. 9. Fig. 10. To the smaller and more common roses only twelve facets are given. Besides the above-mentioned forms, there are the: Huitpan, or single cut. 16 facet " double " 24 " " single brilliant. Cabochon " carbuncle. Star cut, fig. 9. Degree or rose cut, fig. 10. The last two beautiful forms of cutting are frequently given to fine paste or imitation diamonds. Of late years nearly all gems have been cut quite round, and in many instances with a sacrifice of size and brilliancy. [Pg 32] [Pg 33] [Pg 34] [Pg 35] Diamond. The diamond is one of the most precious minerals, and yet it consists of pure carbon, the most common substance that is known, a substance that is present in all animal and vegetable bodies and in the larger number of minerals. When carbon is crystallized the result is the diamond, which is always found in detached crystals, either octahedrons or rhombic dodecahedrons, the planes of the angles being often convex or rounded,—this curving crystal being peculiar to the diamond. The cleavage is perfect, and, parallel to the faces of the octahedron, the fracture is conchoidal or curved. The diamond is not acted upon by acids or alkalies, is infusible but combustible, and burns under heat of a very high temperature. Diamond powder burns readily, but larger pieces are not affected by the blow-pipe. The diamond is a non-conductor of electricity, but acquires positive electricity when rubbed, and retains it for half an hour. After being exposed to the solar rays, the diamond presents a distinct phosphorescence in the dark. It possesses single refraction, but belongs to those bodies which reflect light most strongly, and its magnifying power is much greater than that of glass; it does not polarize light; its lustre is adamantine, and specific gravity 3.5 to 3.6. The diamond is the hardest of all known minerals, ranking No. 10 in Moh’s scale of hardness. White, and the different shades from very light yellow to dark yellow or canary, comprise, according to the popular idea, the colors of the diamond. Yet the diamond is found in green, red, blue, brown, olive, orange, and black, and also in the various shadings of these colors and in opalescent tints. As the limpid or white diamond surpasses all other white stones in the power of its lustre and the magnificence of its fire, so do the colored diamonds outrank the emerald, ruby, sapphire, and other gems of like colors. Colored diamonds, excepting light yellow and brown, are rare, and hence are the most valuable of precious stones. The limpid or perfectly white and the white with a bluish tint are the most sought after, while fine deep golden yellow or canaries and pronounced fancy colors always find a ready market. Diamonds come principally from the mines in South Africa; some are found in Brazil and India, and fewer in Sumatra, Borneo, the Ural Mountains, and Australia. Crystals have also been found in the United States. The amorphous or carbon diamond is found only in Brazil. The pebbles or masses are opaque, steel-gray to black in color, and sometimes weigh 1,000 carats. This carbonate is principally used to point rock-drills and for other engineering purposes. The coarse variety of crystallized diamonds is called bort, and as this is unfitted for gem purposes because of imperfections, it is ground into powder and used for cutting and drilling precious stones. White sapphires, white zircons, white topaz, and rock-crystal sometimes pass for diamonds. The first two are heavier, the topaz lacks brilliancy, and the crystal is lighter than the diamond. It is also the case that these four stones, especially the crystal, are easily scratched by a diamond. The best style of cutting for a diamond is the brilliant, of 66 facets, including the table and culet. The proper proportions of a well cut brilliant is ⅓ for the crown and ⅔ for the culet. The table and culet must also be in proportion to the size of the stone. Corundum. This many-colored mineral, composed of nearly pure alumina, produces gems which in some cases are more valuable even than diamonds. The ruby, sapphire, Oriental emerald, Oriental topaz, Oriental amethyst, Oriental aquamarine, Oriental chrysolite, Oriental hyacinth, star ruby, star sapphire, star topaz, and ruby and sapphire cat’s-eyes are all corundums of different colors. The ruby is a red sapphire, and the Oriental topaz a yellow sapphire, while the Oriental emerald is a green sapphire, etc., etc. In hardness corundum ranks next to the diamond, ranking No. 9 in Moh’s scale. The specific gravity is 3.9 to 4.1, the crystallization rhombohedral, and cleavage basal, the crystals breaking across the prism with nearly a flat surface. In lustre, the corundum is vitreous, its refraction double but not to a high degree, and it is susceptible of electricity by friction, which the polished specimens especially retain for a considerable time. Corundum is unaffected by chemicals, and is infusible alone, but in combination with a flux it melts with difficulty into a clear glass. The chemical composition of precious corundum is: Alumina 98.5 Oxide of iron 1.0 Lime 0.5 100. Thus it will be seen that corundum is composed almost wholly of alumina,—one of the constituents of common clay, [Pg 36] [Pg 37] [Pg 38] [Pg 39] [Pg 40] which, when colored by traces of metallic oxides, chrome, etc., produces a greater variety of precious stones of a high rank than any other mineral. The Ruby. The red sapphire or ruby is the most valuable of the corundum family, and when found of a good color, pure and brilliant, and in sizes of one carat and larger, it is much more valuable than a fine diamond of the same size. Fine rubies larger than 1½ to 2 carats are very rare, and when a fine stone from 3 to 5 carats is offered for sale, the price mounts into the thousands. The color varies from the lightest rose tint to the deepest carmine; that color, however, which has the greatest value is known in commerce as pigeon’s blood, and is the color of arterial blood, or of the very centre of the red ray in the solar spectrum. The imperfections in rubies, as in all corundums, consist largely of clouds, milky spots, and cracks. A perfect ruby is rarely met with, and a stone possessing brilliancy and the true color, even if slightly defective, is considered more valuable than an absolutely perfect ruby of an inferior color. Rubies are found in Siam, Ceylon, Burmah, Brazil, Hindustan, Borneo, Sumatra, Australia, France, and Germany. Where rubies and sapphires are met with it is said that gold is almost sure to be present. Chemists have succeeded in producing minute crystals of rubies and sapphires which, under the microscope, presented the true crystallization of corundums, and upon being tested proved to be of the same hardness as rubies and sapphires; but these specimens were small, and cost very much more to produce than their commercial value. Ruby spinels, garnets, hyacinths, red quartz, burnt Brazilian or rose topaz, and red tourmaline are sometimes passed off for the ruby. The true ruby will scratch all of these stones readily, the spinel is lighter in specific gravity, and has generally a slight tinge of yellow, even in the most pronounced red specimens. The ruby will turn green under the flames of a blow-pipe, but when cooled off, resumes its original color. The garnet and topaz are easily scratched by the ruby, the hyacinth is heavier, and quartz and tourmaline lighter than the ruby. Some so-called reconstructed rubies, recently offered for sale, are of a very fine color, and closely resemble the Oriental gems. The hardness and specific gravity are the same, but they differ in one very important point, namely: they lack the brilliancy of the true ruby. In addition to this lack of fire, a microscopical test discloses formations which will distinguish the manufactured from the natural stone. Sapphire. The blue corundum, ranging in color from the lightest blue to deep blue and black, is the same stone as the ruby, the only difference being in the color. The choicest color is the soft velvety blue, approaching the corn-flower in shade and exhibiting that color vividly by artificial as well as by natural light. The deeper-colored stones are known as male, and the light-colored ones as female sapphires. Although choice sapphires are rare, a much greater quantity of good and large stones are to be had than of rubies, and therefore the price of a large sapphire does not advance in the same proportion as the price of a large ruby. Fancy Sapphires. The Oriental emerald or green sapphire does not approach the beryl or true emerald in depth of color, but because of its superior hardness and brilliancy, added to its extreme rarity, it is the most valuable of green gems. The Oriental amethyst or purple sapphire sometimes reflects a red color by artificial light, and is valued highly as a gem stone; the common amethyst is softer, less brilliant, and loses by artificial light. The various other colored sapphires, such as yellow or Oriental topaz, light green or Oriental aquamarine, greenish- yellow or Oriental chrysolite, and aurora-red or Oriental hyacinth, are all valuable as gem stones when they are pure, well cut, and have pronounced colors—in fact, the name Oriental is given to distinguish the corundums from the less valuable minerals of the same colors which they resemble, but which they greatly surpass in beauty and value because of their brilliancy and superior hardness. Star Sapphires. Asterias or star stones are corundums of three different colors; the star sapphire proper is a grayish blue, the star ruby red, and the star topaz yellow. [Pg 41] [Pg 42] [Pg 43] [Pg 44] [Pg 45]