THE NONMETALLIC MINERALS. 397 



stout prisms, belonging- to the monoclinic system (Specimen No. 15514, 

 U.S.N.M.) Hardness, 2 to 2.5; specific gravity, 1.7. Readily soluble 

 in water; taste sweetish alkaline. 



2. Ulexite ; Boronatrocalcite. 



Composition NaCaB,0.r8H20,= boron trioxide, 43 per cent; lime, 

 13. 8 per cent; soda, 7. 7 per cent; water, 85. 5. Color, white, with silky 

 luster. Occurs usually in rounded masses of loose texture, which con- 

 sist mainly of fine acicular crystals or fibers. (See Specimen No. 

 18128, U.S.N.M., from Rhodes Marsh, Nevada.) Insoluble in cold 

 water, and only slightly so in hot, the solution being alkaline. Hard- 

 ness, 1; specific gravity, 1.65. 



3. COLEMANITE. 



Composition Ca2BgOii.5H20,=boron trioxide, 50.9 per cent; lime, 

 27.2 per cent; water, 21.9 per cent. Color, milky to yellowish- white, 

 or colorless; transparent to translucent. Hardness, 4 to 4.5; specific 

 gravity, 2.41. Insoluble in water, but readily so in hot hydrochloric 

 acid. Priceite and pandermite are hydrous calcium borates closely 

 allied to colemanite, occurring in loosely coherent and chalky or mas- 

 sive forms. (Specimen No. 63362, U.S.N.M.). 



4. BoRACiTE OR Stassfurtite ; Borate of Magnesia. 



Composition Mg^ClBigOso,^ boron trioxide, 62.5 per cent; mag- 

 nesia, 31.4 per cent; chlorine, 7.9 per cent. Color, white to yellow or 

 greenish. In crystals transparent to translucent. Crystals cubic and 

 tetrahedral. Insoluble in water; readily soluble in hydrochloric acid. 

 Hardness, 7; specific gravity, 2.9to3. (Specimen No. 64742, U.S.N.M., 

 from Stassfurt.) 



Localities and mode of occurrence. — As has been stated by Kemp^ 

 the Great Basin region of the United States contains, along the Nevada- 

 California border at least ten salines or marshes which have been found 

 to hold boracic deposits. The marshes are regarded as the beds of 

 relatively restricted lakes which received boracic water, probably from 

 hot springs. Volcanic phenomena are abundant and were doubtless 

 the stimulating causes. Besides borax, ulexite (borate of lime and 

 soda) and priceite (borate of lime) are found commingled with more 

 or less gypsum, carbonate, chloride, and sulphate of soda and various 

 other alkaline salts. The best known of the salines in Nevada are 

 Teels Marsh, Columbus Marsh, Fish Lake Valley, and Rhodes Marsh, 

 all in Esmeralda County. These cover an area of thousands of acres, 

 but the productive portions are comparatively limited. In Churchill 

 County, this same State, there is a minor deposit at Salt Wells (Speci- 

 men No. 15522, U.S.N.M.). In California there is an important 

 deposit known as Searles Marsh, in San Bernardino County, and a vein 



iThe Mineral Industry, 1892, p. 43. 



