How and why were these sapphires deposited in globular forms when the law of crystallization is so rigid and inflexible? This is a question which requires considerable assurance to answer, in the view that they are original depositions; but Nature offers many examples to sustain the theory if we search her domain; for instance, how were the rounded nodules of flint formed in the chalk-beds? Their shape is not due to attrition, and their peculiar arrangement forbids the belief that they have been rolled or abraded by the agency of water. In the interior of solid ledges we find nodules of quartz with rounded edges, as though they had been exposed to some dissolving agency or abrading force; yet they have been beyond the reach of external violence. Hence we must conclude that their globular form is perhaps due to some deviation in the usual process of deposition or crystallization. Huronite occurs in spherical masses in hornblendic bowlders; and we may find nodules of tourmaline in the interior of the most perfect crystals of the mineral. There are other examples.
The Cingalese do the mining and sell the gems to Moors, who resort to Ratnapoora to attend the jewel fair, which is held at the annual Buddhist festival of the Pera. Purchasers not only from all parts of Ceylon, but India, come to buy gems at this time. It has therefore become the great jewel mart of the world; and one can find there many of the rare and beautiful gems found in other parts of the world: the emeralds of Peru, the topazes of Brazil, the opals of Honduras, the turquoises of Persia, the jade of China; in fact, most of the gems that have a commercial value, or any tradition attached thereto, are to be found at these fairs. They are of greater importance than the famous fairs at Novgorod in Russia, to which the gems and precious stones of Northern and Central Asia are annually sent.
The Hindoos are the best buyers of gems of all the nations of the world. Their rajahs and princes pay the highest prices for the paragons; and the poor native had rather invest in a gem, which to his simple belief adds to his security and happiness, than hoard gold coins, which are no better for concealment. The Moors are also generally the lapidaries. The tools which they use in cutting the gems are rude and primitive, and often the stones are much impaired under their hands; but some of the workmen are skilful and are able to copy with exactness the most perfectly cut gems of the European lapidaries. Workmen of the inferior class may be found in the little towns all over the island; but the artists of the first rank are located at Callatura and Colombo. Immense numbers of garnets, zircons, and inferior sapphires, with other gems, are cut by these rude artisans, who place but little value on their time, and therefore work for a trifle. These precious stones are then sold on the island or exported to foreign lands, but are generally taken to India by travelling merchants, who exchange them for produce or money. The demand is so great from the populous Mohammedan nations, that many of these gems are really higher in price in India than in the gem marts in Europe, as in the time of Tavernier, three hundred years ago. Another potent reason prevents the market from being glutted: the Hindoo parts with his gem reluctantly, and only in case of necessity or in hope of greater gain; and the wealthy Parsee prides himself upon his display of gems, as well as upon his degree of caste. The quantity of gems treasured up by the inhabitants of India must be immense.
The composition of the sapphire, when found in the clear, transparent form, is pure alumina. Its degree of hardness is 9, being inferior only to the diamond; and its range of colors is very extensive, embracing most of those seen in the solar spectrum. Its specific gravity varies from 3.9 to 4.3; and, with the exception of the zircon, it is the heaviest of all the gems. It is also compact and exceedingly tough in its texture, and resists the shocks and wear of time better than any other gem, not excepting even the diamond, which is harder, but far more fragile. In point of brilliancy, it is below the zircon, garnet, and the spinel, its refractive index being 1.77 to 1.79. This mineral possesses remarkable electrical properties, but not so marked in degree as in the tourmaline or topaz; when this property is excited in the polished specimen, the attraction continues for a considerable length of time. The property of double refraction is not often very distinct, and by means of this peculiarity it is sometimes detected from the spinel.
The term corundum is now applied to the coarser and less transparent kinds of the stone, which have been used as a polishing material from time immemorial. The granular variety known as emery is largely mixed with iron ores, and is far inferior to the transparent and purer varieties as an abrading agent. It is always of a blackish or dark-gray hue, and is often mistaken for iron ore. Asia Minor furnishes nearly all of the emery used in the arts. It is found there in masses or bowlders, either free or in granular limestone. In the United States it is found along the gold belt in the Southern States; and in Chester, a town of Massachusetts, it occurs in a large and valuable vein associated with diaspore, ripidolite, etc., which generally accompany it. At this mine at Chester, translucent sapphires of bi-pyramidal form are sometimes found. Dr. C. J. Jackson found one small blue crystal quite transparent and doubly terminated.
The corundum belt of the United States has been traced, with wide intervals, however, from Philadelphia to Northern Georgia. All along this distance of several hundred miles, masses of corundum, more or less transparent, have been found during the past forty years, but active search failed to reveal the mineral in its matrix. A few years ago exploration in the extreme southwestern part of North Carolina discovered the long-looked-for corundum in situ. It was found on the side of a mountain, in a mica-like substance called ripidolite. The corundum from this locality appears in geodes and also in well-marked crystals, ranging from small size to even the weight of three hundred pounds. It is often of perfect transparency, but may be translucent or opaque. The transparent crystals and masses, although possessing limpidity, are traversed in all directions with cleavage planes, which prevent their use in ornamentation. The colors are also irregularly distributed in patches, clouds, or in thin veneers; many specimens have been seen of variegated hues,—red, white, yellow, and blue,—and even the whole of these colors have been seen in a single specimen.
From the great number of specimens submitted to our examination we have no hesitation in saying that gems cannot be quarried at will from these mines. The inequality of color and the frequency of cleavage planes will forbid. Small gems of few grains weight may be cut from some of the transparent masses if the clear portions are selected with care, and cut with that skill which is required in the shaping of gems whose color is unequally distributed. But it is doubtful if fine gems are found in this formation, for the conditions which deposited the corundum here, and the more perfect specimens in the true gem strata elsewhere, are quite different.
The colors of the North Carolina corundum are often very fine, and we have seen specimens of a superb blue that retain their hues by candlelight. None of the reds we have ever seen have the true pigeons’-blood tint, but are tinged with blue, and are therefore of a finer shade when seen by artificial light than by daylight. The yellows are also of a decided shade, and generally form a portion only of the crystal or mass of sapphire.
Some fine crystals have been found here, but we have seen none so perfectly crystallized as the pyramidal specimens from the Asiatic mines. Several large crystals have been exhumed, one of which weighs three hundred pounds, and is well defined in its form of crystallization. It is now preserved in the valuable cabinet of Professor Shepherd, of Amherst College.
A few years ago the gold-miners, while seeking for gold in the river-beds and alluvial deposits among the mountains of Montana, observed little transparent crystals of stone among the nuggets and flakes of gold, as they cleared out their rude apparatus used in washing the auriferous soils. But little notice was taken of these limpid stones, as their colors were generally faint; but the observing gold-seekers remarked their great weight and the remarkable coldness to the touch, as they passed them around to each other in wonderment. For a long time the miners flung these minerals away with other refuse, unconscious of their character or their value; but one day there appeared in the dark sands of the gold-pans a stone which flashed forth such brilliant red gleams as to excite anew the curiosity and cupidity of the miners. This discovery led to inquiry, and the gold-seekers learned too late concerning the value of the treasures they had carelessly thrown away. Afterwards the gems were preserved and sent with the gold-dust to the States. They proved to be sapphires. Some of them were finely crystallized in long, regular prisms, but the most of them were without definite form. None of the several hundred specimens that have been submitted to us exhibited smooth faces, like the brilliant facets of crystals found in cavities of the crystalline rocks or in the gem mines of Ceylon; but all exhibited a roughness of the exterior, as though they had been abraded by aqueous action.