406 REPORT OF NATIONAL MUSEUM, 1899. 



the baritc is found in loose, disconnected masses embedded in a residual 

 clay, and the process of mining is resolved into merely digging so long 

 as the yield is sufficient to pay expenses. 



Preparation and mes. — The mineral is washed and ground like grain 

 between millstones and used as an adulterant for white lead or to give 

 weight and body to certain kinds of cloth and paper. 



According to a writer in the Mineral Resources of the United States 

 for 1885, the '* floated" or " cream -floated " barite used for paint is 

 prepared as follows: The crude mineral as mined is first sorted by 

 hand and cleaned, after which it is crushed into pieces about the size 

 of the tip of one's finger. Next, it is refined by boiling in dilute sul- 

 phuric acid until all the impurities are removed, when it is washed by 

 boiling in distilled water and dried by steam. It is then ground to 

 flour, mixed with water, and run through troughs or sluiceways into 

 receiving vats, whence it is taken, again dried by steam, and barreled. 

 This cream-floated barite is quoted as worth about $30 a ton, while 

 the crude material is worth only about one-fourth as much. 



Sources. — The principal sources in the United States are Lynchburg, 

 Hurt, Toshes, and Otter River, Virginia; Sandy Bottom and Hot 

 Springs, in North Carolina, and Cadet, Old Mines, Mineral Point, 

 Morrellton, and Potosi, in Missouri. A small amount is imported 

 from Mackellar Islands, Lake Superior. The total production for 

 1897 was some 27,316 tons, valued at $4 a ton.' 



2. Gypsum. 



Composition CaSO, + 3 H^O, = sulphur trioxide 4:^.^ per cent, lime 

 32.5 per cent, water 20.9 per cent. The natural mineral is often quite 

 impure through the presence of organic, ferruginous, and aluminous 

 matter, together with small quantities of the carbonates of lime and 

 magnesia (see analysis, p. 407). Specific gravity 2.3, hardness 1.5 to 

 2. Color usually white or gray, but brown, black and red through 

 impurities. The softness of the mineral, which is such that it can be 

 easily cut with a knife or even by the thumb nail, is one of its most 

 marked characteristics. Three principal varieties are recognized, (1) 

 the crystallized, foliated, transparent variety, selenite (Specimens Nos. 

 53593, 53608, 62089, U.S.N.M.), (2) the fine fibrous, often opalescent 

 variety, satin spar (Specimen No. 62477, U.S.N.M.), and (3) the com- 

 mon massive, finely granular variety, gypsum (Specimen No. 53348, 

 U.S.N.M.). When of a white color and sufficiently compact for small 

 statues and other ornamental works, it is known as alabaster (Specimen 

 No. 63394, U.S.N.M.), though this name has unfortunately become 

 confounded with the calcareous rock travertine and stalagmite.^ 



iThe Mineral Industry, VI, 1897, p. 57. 



2 See The Onyx Marbles, their Origin, Uses, etc., Report of the U. 8. National 

 Museum, 1893, pp. 539-585. 



