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PRECIOUS STONES

SAPPHIRE

OCCURRENCE

According to his report these deposits are situated in a small upland valley in the upper part of the district of Padar, about thirteen days journey south-east of Srinagar, the capital of Kashmir, a few miles to the east of the village of Machel, and a little west-north-west of the village of Soomjam. Soomjam is higher than any other village on the southwestern slopes of the lofty Zanskar range. It is about half a day journey down from the Umasi Pass, and has an altitude of 11,000 feet. It lies in latitude 33° 25' 30" N., and longitude 76° 28' 10" E., on the Bhutna River, a tributary of the Chinab.

The valley in which the sapphires are found is 1,000 yards long and 400 yards wide at its lower end; it has an elevation of 13,000 feet above sea level, and its floor rises towards the northwest, the average angle of slope being about 20°. The first find have been made in the sapphire-bearing rock, which forms a precipice at the head of the valley. This rock, which was laid bare by a landslip, is at an altitude of 14,800 feet, and lies very near the limit of perpetual snow. A large number of gems were at first won from the solid rock; very soon, however, it was discovered that they existed in equal abundance in the loose detrital material weathered from these rocks and deposited on the floor of the valley. Veins of granite penetrate the rocks of the district, mainly mica-schists and garnetiferous gneiss with interfoliated crystalline limestone, and it is in these veins that the sapphire, associated with an abundance of dark-brown tourmaline, is found. The material formed by the weathering of the granite is laid down in the valley as a white bed of little thickness, and is described as being overlain by a reddish-brown earth. The gems were picked out by hand from this deposit "like potatoes" though they ware, of course, also won by washing. The dark-brown tourmaline, mentioned above as being present in the granite veins, is also found in these secondary deposits.

The fine blue color of the sapphires of this locality first attracted the attention of the inhabitants, who, not knowing the value of the stones often used them for striking fire. They were so abundant at first that large numbers were collected by the natives and sold to the gem merchants of Simla and Delhi, who, supposing them to be blue quartz or amethyst, purchased them very cheaply. When their true nature became known many expeditions were sent out to the Zanskar range with the object of collecting as many of these valuable stones as possible. The prices, of course, rose, and very quickly reached the figure at which sapphire is usually sold, namely, about £20 per ounce. Later on the stones fell again in value owing to the large number, which were put on the market. Soon the Maharajah of Kashmir, in whose dominions the deposit is situated, began to interest himself in the matter. Those persons who had already found stones were allowed to retain them, but duly licensed individuals, who had to pay for the privilege, could only make any further search. This arrangement still holds good.

The sapphires found in the Zanskar range are frequently in well-developed crystals, of the forms shown in Fig. e to i. Numerous dark-brown or green tourmalines of small size are often observed enclosed in, or growing on the surface of, the crystals of sapphire. The crystals arc sometimes very large, specimens suitable for cutting having been found measuring 5 inches in length and 3 inches in thickness, while a few arc said to have attained a length of a foot. Irregular grains and fragments of the gem are frequently met with, but many of these are probably due to the fracture of crystals during their extraction from the mother-rock. The stones found in the loose weathered material on the floor of the valley are more or less rounded, showing that they have been transported some distance by running water. Some are of considerable size, weighing 100 or even 300 carats.

The crystals of sapphire are often bluish-white or bluish-gray, but specimens of a finer and richer color are also frequently found. Single crystals often show a difference of color in different portions; thus the center of a crystal may be of a fine blue color, and the two ends colorless. The majority of the stones found here possess, wholly or in part, a milky cloudiness; silkiness of luster is also a common fault. Only transparent and finely colored stones are valuable as gems. Large cloudy crystals often have a small portion clear and transparent, which is carefully cut away by the lapidary and transformed into a gem. The yellow, brown, and red varieties of corundum are rare at this locality.

These mines are not the only places in this remote region where sapphires worth cutting have been found. At some distance away, but still in the same neighborhood, are several places at which sapphire occurs under exactly similar conditions as far as is known. Thus, stones, which were not at first recognized as sapphires, were brought down from the Sacha Pass to the gem-market at Delhi, and others have been found in the gneiss and mica-schist of the upper Raini valley, below the Hamta Pass in Kulu, Punjab, as well as at other places.

All varieties of precious corundum-ruby, sapphire, "oriental topaz", "oriental emerald", etc. are found in the United States of North America, being especially abundant in two particular regions. The first of these regions includes the western portions of North Carolina and of South Carolina and extends into Georgia and Alabama. Almost all the precious corundum found in this region comes from Macon County in North Carolina, where the crystals, which are usually well developed, are enclosed in an olivine-rock (dunite). The occurrence of corundum in rocks other than dunite in North Carolina, and especially at Cowee Creek in Macon County, has already been dealt with under ruby. In these localities the pure mineral often forms the nucleus of large masses of common corundum. In the Culsagee mine on Corundum Hill, near Franklin in Macon County, a crystal weighing 311 pounds was once found. This, however, was not of gem quality and was colored partly red and partly blue. At the same mine rubies, sapphire, "oriental topaz", and a few "oriental emeralds", etc., suitable for cutting as gems, have been found. Fine star-stones occur here also, as well as in Delaware County, Pennsylvania.

The other region, which is especially rich in precious corundum, is situated in the west. Sapphire and other color-varieties of corundum have been known since 1865 to occur in the neighborhood of Helena on the upper reaches of the Missouri river, in the State of Montana, being first discovered during the process of gold-washing. Again the true nature of the stones was not at first recognized, and they were sold at much below their actual value. Since 1891 these deposits have been systematically worked for gold, and at the same time large numbers of the precious stones have been collected. They are found in masses of glacial debris known as" bars", which are laid down on the sides of the valleys parallel to the river-courses and at a height of 300 feet above the present high-water level of the upper Missouri. These glacial sands and gravels containing gold overlie black shales, probably of Lower Silurian age, which are associated with limestones, quartzite, and rocks of igneous origin. It is in the lowest layer of these sands and gravels, with a thickness of only a few inches, that the sapphire is principally found. The sapphires ware most abundant at Eldorado Bar, Spokane Bar, French Bar, and Ruby Bar, and these deposits ware being worked. Spokane Bar near Stubb's Ferry, twelve miles to the east of Helena, was approximately the central point of this district, which extends along the Missouri for at least fifteen miles and embraces an area of certainly no less than eleven and a half square miles.

The sapphires frequently occurred as well-developed crystals, having the form of a short hexagonal prism with basal planes, an unusual type for this gem. Irregular grains ware also found, which like the crystals, are more or less rounded. Neither crystals nor grains attain to any considerable size, measuring at the most from 1/4 to 1/2 inch in diameter and rarely exceeding 9 carats in weight. Though small in size the stones ware abundant in number, as evidenced by the fact that an acre of the deposit at Eldorado Bar yielded no less than 2,000 ounces of sapphire. Many of these stones, however, were unsuitable for cutting, since the predominant tints of the sapphires of this locality are all pale.

The colors, though almost always pale in shade, show great variety of tint, red, violet, yellow, blue, green, bluish-green, and all possible intermediate colors being met with. Bluish-green and green corundum is especially abundant, while the pure blue and the red varieties are absent. Occasionally a stone with it red nucleus and a border of another color is met with. Some green and blue stones appear red by artificial light. Almost all the color-varieties of corundum from this region, which are suitable for cutting, have a peculiar metallic sheen, which is very characteristic and is not seen in stones from any other locality. They are remarkable also for the brilliancy of their luster, and, according to the statements of lapidaries, are especially hard.

Corundum is associated in these glacial sands with many other minerals, among which are crystals of white topaz not exceeding 1/4 inch in length, fine ruby-red garnets the size of a pea (which have often been mistaken for true rubies), kyanite, cassiterite in small, rounded grains (stream-tin), iron-pyrites altered to limonite, chalcedony, and small rounded fragments of calcite.

As already mentioned, the rocks occurring in situ in the district and underlying the gemmiferous sands are penetrated by dykes of igneous material. In one of these dykes, consisting of mica-augite andesite, crystals of sapphire, garnet (pyrope), and sanidine have been found; and it has been argued from this that in every case the sapphires originated in similar situations and have been set free by the weathering of the igneous rock. This origin for the sapphire is not universally accepted, although parallel cases may be found in the occurrence of fine blue sapphire in the volcanic rocks of other regions, such, for example, as the basalts of Unkel on the Rhine, Niedermendig on the Laacher See, Calvarienberg near Fulda, and Expailly near Le Puy-en-Velay in France, etc. Also sapphires have been found at Yogo Gulch in Fergus County in the State of Montana, and seventy-five to one hundred miles east of the Missouri bars. According to G. F. Kunz and others they occur in a yellow earthy material, which may owe its origin to the weathering of an igneous rock. The blue stones vary in shade from light to dark, some being of the true sapphire or cornflower-blue, while there are others which incline to an amethyst or almost ruby shade of red. The crystals are rhombohedral in habit, and in this respect differ from the sapphires found near Helena.

The amount of corundum of a quality suitable for cutting, which comes into the market from Australia, is not altogether insignificant. The mineral is found in gold-sands with diamond and in stanniferous and other similar sands and gravels in Victoria, South Australia, Queensland, and especially in New South Wales. In the last named State, sapphires are found in the north-east corner in the New England district, especially in the neighbourhood of Bingera and Inverell, and indeed at all the localities which have been already mentioned for diamond. Sapphire occurs here under exactly the same conditions as does the diamond, and it is even more widely distributed. An occurrence of the stone in Tasmania has also been reported.

Australian sapphires, as a rule, are too dark to be of much value as gems; they vary from perfect transparency and absence of color through various shades of blue and gray to almost absolute opacity and dark blue color. Crystals showing a fine sapphire-blue color are met with occasionally, and fine star-sapphires are not uncommon. A few rubies are found, but corundum of a fine green color, that is "oriental emerald", is more abundant, every hundred stones always including two or three specimens of "oriental emerald". The original crystalline form of the stones, a hexagonal bipyramid (Fig. e) is frequently well preserved, but more often they are in the form of irregular grains or rounded pebbles, like the other constituents of the sands. From a commercial point of view the Australian output of sapphires is unimportant.

[ RUBY  1  2  3  4  5  SAPPHIRE  7  8  9  EMERALD  11  12  13  AQUAMARINE  15  ]
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This document is in the public domain.

March, 2011