Precious Gem stones production in 1911 Page 81



	1054	MINERAL RESOURCES.

	quantities of other elements may be present and in some stones influence the color. Thus, beryl containing caesium is generally colorless and very brilliant; the presence of lithium produces the pink beryl, and chromium the emerald. Other color varieties of beryl are aquamarine, blue beryl, and golden beryl. A small per cent of chromium oxide is sufficient to impart a rich emerald-green to beryl. According to Bauer,¹ an analysis by F. Wohler of Colombian emerald gave 0.186 per cent chromium oxide. Beryl crystallizes in the hexagonal system and commonly occurs in six-sided prismatic crystals terminated by the base with or without other faces. In emerald simply the prism faces and base are the most common. Beryl is nearly always found crystallized, even when "frozen" in hard rock. Crystals that have developed in cavities are in some cases beautifully developed. The following notes on the occurrence of emeralds in Colombia, Egypt, the Ural Mountains, and Salzburg Alps are taken from Max Bauer.¹ In Colombia emeralds occur in calcite veins and nests in dark bituminous limestone. The limestone overlies red sandstone and clay slate of Cretaceous age. The calcite may be dark with bituminous matter or clear like Iceland spar. Associated with the emeralds are fine quartz crystals, both colorless and green, pyrite, green gypsum, black dolomite, and parisite, a fluo-carbonate of cerium, and other rare metals. In Upper Egypt the emeralds occur in dark mica schist interfoliated with talc schist, and at one locality these rocks contain also augite and hornblende. The occurrence in the Ural Mountains is said to be very similar. In the Salzburg Alps the matrix is described as somewhat similar and consists of finely granular dark brown and greenish mica schist interfoliated with chlorite and hornblende schist. The emeralds found in Maine and Connecticut were associated with pegmatite. At the emerald-hiddenite mine in Alexander County, N. C, emeralds have been found in pockets and cavities in veins cutting biotite gneiss. The gneiss has been strongly compressed and folded while in a plastic condition. In the neighborhood of the veins it has been highly silici-fied by the addition of much quartz which, along with muscovite, rutile, pyrite, etc., has replaced the biotite and feldspar. The minerals filling the veins are quartz, calcite, dolomite, muscovite, rutile, black tourmaline, pyrite, cnalcopyrite, monazite, aquamarine, emerald, and hiddenite. There are numerous veins near the mine which carry common beryl, aquamarine, and quartz, but emeralds and hiddenite were found in only a few veins. Hiddenite, the emerald-green spodumene, was the chief mineral of value obtained from this locality, though some fine emerald crystals were found. According to Arthur Keith,² at the Crabtree Mountain locality in Mitchell County, N. C, the emeralds occur in pegmatite inclosed in mica gneiss. A few feet east of the vein is a body of hornblende gneiss. The pegmatite has a northerly strike and dips 45°-50° E. It is composed mainly of feldspar, quartz, black tourmaline, and beryl, and incloses horses of biotite-tourmaline schist. The emeralds occur i Precious stones (translation by L. J. Spencer), Charles Griffin & Co., Ltd., London, 1904. » Mount Mitchell folio (No. 124), Geol. Atlas U. S., U. S. Geol. Survey, 1905.