RUBY. This name is applied by lapidaries and jewelers to two distinct minerals, which may be distinguished as the true or Oriental ruby and the spinel ruby. The former is a red variety of corundum or native alumina, of great rarity and value, while the latter is an aluminate of magnesium, inferior to the true ruby is hardness and much less esteemed as a gem stone. With ancient writers the confusion was even greater, for they appear to have classed together under a common name, such as the carbunculus of Pliny or the of Greek writers, not only our two kinds of ruby but also garnets and other inferior stones of a brilliant fiery color. By modern mineralogists it has come to be understood that when the word ruby is used without any qualifying prefix the true or Oriental stone is invariably indicated.
The Oriental ruby, like all other varieties of corundum, crystallizes in the rhomboheral system; but, as it usually occurs as small pebbles or rounded fragments, the crystalline form can rarely be traced. Its color varies from deep cochineal to pale rose red, in some cases inclining to purple, the most valued tint being that know to experts as pigeons blood color. On exposure to a high temperature the ruby becomes green, but regains its original color on cooling-a behavior which is consistent with the supposition that the stone owes its color to the presence of oxide of chromium, and indeed in artificial rubies the required tint is always obtained by the use of some compound of chromium. When a ruby of the most esteemed color is properly viewed through a dichroiscope, the color is resolved into a carmine and an aurora red, or red inclining to orange. By this test the true ruby may be distinguished from spinel and garnet, since these minerals crystallize in the cubic system and therefore are not dichroic. Another mode of distinction is suggested by the high density of corumdum: the specific gravity of the true ruby reaches or even rises slightly above 4, and thus greatly exceeds that of either spinel or garnet. But perhaps the simplest test is afforded by its great hardness (H=9): the sharp edge of a corumdum crystal will readily scratch either a spinel or a garnet, but has no effect on a ruby. The true ruby has a very high index of refraction (u = 1.78), and to this character is due the remarkable luster of the polished stone. Mr. Crookes has shown that the ruby is brilliantly phosphorescent when subjected to radiant discharge in a properly exhausted vessel, and curiously enough the red light emitted is equally vivid whatever be the color of the corumdum under experiment. The microscopic structure of the ruby has been studied by Mr Sorby, who finds that the stone contains fluid cavities and numerous crystallized enclosures of other minerals (proc.. Roy. Soc., xvii., 1869, p. 291).
The oriental ruby is a mineral of very limited distribution, its principal localities being confined to the kingdom of Burmah. The most important ruby mines are situated at Kyat Pyen, about 780 miles to the north-east of Mandalay; there are also mines at Mookop, a little farther north, and others in the Sagyin Hills, within 16 miles of Mandalay. In all these localities the rubies occur in association with sapphires and other precious stones, forming a gem-bearing gravel which is dug up and washed in very primitive fashion. By far the larger number of the rubies are of small size, and the larger stones are generally flawed. All rubies exceeding a certain weight were the property of the king of Burmah. The mines were jealously watched, and it was difficult for Europeans to obtain access to them; but some of the Ava workings were visisted and described many years ago by Pere Giuseppe dAmato, and more recently those near Mandalay have been described by Mr Bredmeyer, who was officially connected with them (Ball). It is stated in the older works on mineralogy that rubies occur in the Capelan Mountains, - the Kyat Pyen locality. In peninsula India there are but few localities that yield rubies, but they have been reported from the corumdum mines of the Salem district in Madras and from Mysore. In Ceylon they occur with sapphires, but are rarer than those gems, and the Ceylon rubies are not usually of good color. Rubies have been brought from Gandamak, in Afghanistan, but most of the stones reputed to be Afghan rubies.
In 1871 some remarkable deposits of corumdum were discovered by Col. C.W. H. Jenks in Macon co., North Carolina. Rubies, sapphires, and large pebbles coarse corumdum were found in the bed of a river near a large mass of serpentine which afterwards became known as Corumdum Hill, and these pebbles were eventually traced to certain veins in the serpentine. The corumdum occurred crystallized in situ, but was rarely of such a color as would entitle it to be called ruby. Mr G. F. Kunz, who has lately written an article on American precious stones, states that rubies and sapphires have also been found at Vernon, New Jersey; near Helena, Montana; at Santa Fe, New Mexico; in southern Colorado, and in Arizona.
Australia has occasionally yielded true rubies, but mostly of small size and inferior quality. In Victoria they have been found in the drifts of the Beechworth gold fields and at the Berwick tin mine, Wallaces Creek; while in New South Wales they occur at Mudgee, in the Cudgegong and some of its tributaries, and at Tumberumba, co. Wynyard. A magenta-colored turbid ruby from Victoria is known under the name of "barklyite."
The "star ruby" is a rather cloudy variety from Ceylon, exhibiting when cut en cabochon a luminous star of six rays, reflected from the convex surface of the stone.
The largest ruby known inEurope is said to be one of the size of a small hens egg, which was presented by Gustavus III. of Sweden to the empress of Russia on the occasion of his visit to St. Petersburg. Rubies of larger size have been described by Tavernier and other Oriental travelers, but it is probable that in many cases spinels have been mistaken for true rubies. There seems no doubt that the great historic ruby set in the Maltese cross in front of the imperial state crown of England is a spinel. This stone was given to Edward the Black Prince by Pedro the Cruel, king of Castile, on the victory of Najera in 1367, and it was afterwards worn by Henry V. at the battle of Agincourt, when it narrowly escaped destruction
The spinel ruby has been described in the article MINERALOGY (vol. xvi. p. 386. sp. 93). The spinels used for jewellery are mostly obtained in Burmah, where they occur as octahedral crystals or as water-worn pebbles in association with the true ruby, for which they are often mistaken. They are also found in the gem-bearing gravels of Ceylon, Victoria, and New South Wales. The delicate rose-pink variety known as balas ruby was worked for centuries in Badakhshan, but the operations appear yo have been suspended of late years. The mines are situated on the river Shighnan, a tributary of the Oxus. It is commonly said that the name "balas" or "balash" is a corruption of Badakhshan, while others derive it from Balkh.
The Oriental ruby has always been esteemed of far higher value than any other precious stone. A ruby of perfect color, weighing five carats, is worth at the present day ten times as much as a diamond of equal weight (Streeter). As the weight of the stone increases, its value rapidly rises, so that rubies of exceptional size command enormous prices. There is consequently much temptation to replace the true stone by spinel or garnet or even paste. By means of oxide of chromium and excellent imitation of the color of the ruby is obtained; and though the ordinary "strass," or fine lead-glass, is very soft, and therefore soon loses its luster, it is yet possible to produce a paste consisting of silicate of alumina which is almost as hard as rock crystal.
It is an interesting fact that the chemist has frequently succeeded in causing alumina to assume artificially many of the physical characteristics of the native ruby. As far back as 1837 M. Gaudin reproduced the ruby on a small scale by exposing ammonia-alum to the heat of the oxyhydrogen blowpipe, whereby he obtained fused alumina which was readily colored by the addition of oxide of chromium. A different method was followed by Ebelmen. He dissolved alumina in boric acid at a high temperature, and on the cooling of the mass obtained the alumina in a crystallized form; while if chromate of ammonium was present the crystals became veritable ruby. MM. Sainte-Claire Deville and Caron heated a mixture of fluoride of aluminium, fluoride of chromium, and boric acid, and thus obtained a fluoride of boron, which, being volatile, readily escaped, and left a solid residue of alumina colored by the chrome. These, however, were only laboratory exeroiments, and it was reserved for MM. Fremy and Feil, in 1878, to reproduce the ruby and sapphire on a scale suggestive of some commercial importance. By heating a mixture of artificial alumina and red lead in a fireclay crucible, they obtained a vitreous silicate of lead (the silica being derived from the crucible) and crystallized alumina, while the addition of bichromate of potassium caused this alumina to assume the coveted tint of the ruby.
For a general description of the ruby see E. Jannettaz, Diamant et Pierres Precieuses (1881); Kluge, Handbuch der Edeisteinkunde (1860); Schrauf, Edfeisteinkunde (1869); Church Precious Stones (1883); Streeter, Precious Stones and Gems 4th. Ed., 1884). For Indian localities see Balls Economic Geology, being vol., iii. of the Manual of the Geology of India (1881); for Australian localities. Liversidges Minerals of New South Wales (2d ed., 1882); for United States rubies, Quart, Jour. Geol. Soc. Lond., vol. xxx. 1874. p. 303, and American Jour. Science, ser, iii. vol. iv. 1872, pp. 109, 175, and Kunzs article in Mineral Resources of the United States, by A. Williams, jun (1883). For the history of the stone consult Kings natural Hist. of Precious Stones (1865), and for artificial rubies, Comptes Rendus, vol. lxxxv. 1877m p, 1029. (F.W.R.)
The above article was written by: Frederick W. Rudler, F.G.S., Curator and Librarian of the Museum of Practical Geology from 1879; of the Museum of Practical Geology, Jerymn Street, 1861-76; assistant director of Ure's Dictionary of Arts and Manufactures; joint author of Stanford's Europe.