CATALOGUE OF GEMS. 507 



it was first broiig-ht ])v u Bucharian morchant, Achir Mahmed, after 

 whom it was called Achirite. Fine crA'stals are found at Mindouli, 

 near Comba, the French Congo, whence the name Congo emerald. 

 Brilliant crystals are found at the copper mines near Clifton, Graham 

 County, Arizona. 



One hundred parts contain: Copper oxide. 50.4; silica. 38.2; water, 

 11.4. 



DUMORTIERITE. 



Dumortierite occurs commonly in tilu'ous to columnar aggregates 

 and massive; rarely in distinct orthorhombic crystals. Luster, vitre- 

 ous. Hardness, 7. Specific gravity. 3.26. Color, strong smalt blue 

 to greenish blue; strongly pleochroic. being colorless, reddish violet, 

 and deep ultramarine in the several directions. The fibrous kinds, 

 when cut cabochon with sufficiently high summits, will often aiford the 

 " cat's-eye " ray. In composition the mineral is essentially a basic 

 aluminum silicate, containing in 100 parts: Silica, 30.6; alumina, 69.1:. 



ENSTATITE. 



BROXZITE HYPERSTHENE. 



Enstatite, bronzite, and hypersthene are orthorhomliic pyroxenes 

 occurring commonly crystalline, massive, fibrous, lamellar, or foliated. 

 Their hardness does not exceed 6; their specific gravity. 3.. 5. and their 

 colors include the various shades of green, gra}', brown, white, and 

 black. When cut cabochon across the fibers they will all afl'ord the 

 " cat's-eye-' ray. 



Enstatite is yellowish, grayish, or greenish white; has a vitreous to 

 pearly luster; a specific gravity, of 3.10 to 3.13; a hardness of 5.5, and 

 is someAvhat l)rittle. In composition it is essentially a magnesian sili- 

 cate containing in 100 parts: Silica, 60; magnesia, 10. 



Bronzite is grayish to olive green and brown in color; has an ada- 

 mantine pearly to a metalloidal or bronze-like luster; a specific gravity 

 of 3.1 to 3.3, and a hardness of 5.5. In composition it is an enstatite, 

 having its magnesium in part replaced by iron. Bronzite and enstatite 

 are common constituents of peridotites and the serpentines derived 

 from them; occurring also in the crystalline schists. 



HyyerstKene is dark ])rownish green, grayish black, greenish black, 

 and pinchbeck brown, occasionally marked ^^\ a play of color resulting 

 from included labradorite. Luster, pearly on cleavage face and fre- 

 quently exhibiting a peculiar metalloidal efl'ect; hardness, 6; specific 

 gravity, 3.1 to 3.5. 



Hypersthene, associated with la))radorite, is common in certain 

 granular eruptive rocks, as noryte and gabbro. Iji composition it is 

 analogous to an enstatite in which the magnesium has in part been 

 replaced by iron, often in the proportion of 1: 1. 



