thp: nonmetallic minerals. 411 



structures arc, liowcvor, stated to have hoon built of this stoiM^ at Fort 

 Dodov, in Iowa. (Spocinien No. 2()8()4, U.S.N.M.) The variety satin 

 spar is sometimes used for small ornamentations, but it is only the 

 snow-white variety (alabaster) that is of any economic importance as 

 an ornamental stone. The main use of alabaster is for small statues, 

 vases, fonts, and small columns; it is too soft for exposed positions 

 where subjected to much wear. At present there are not known any 

 deposits of alabaster within the limits of the United States which are 

 of sufficient purity and extent to be of commercial value. A large 

 share of the alabaster statuettes now on our markets are of Italian 

 make as well as of Italian materials. 



In preparing the gypsum for market the stone is tirst broken in a 

 crusher into pieces of the size of a hickory nut, after which it is ground 

 between millstones (French buhrstones) to a proper degree of fineness 

 and then put up in hags or barrels, if designed for land plaster; if for 

 stucco it is calcined after being ground. This process is in Michigan 

 carried on in large kettles some 8 feet in diameter, and capable of hold- 

 ing about 14 barrels at a charge. The powder is heated until all the 

 included water is driven off, being subjected to constant stirring in 

 the meantime, and is then drawn oft' through the bottom of the kettles 

 and conveyed by carrying belts and spouts to the packing room.^ 



Under the name of "terra alba" (white earth) ground gypsum is 

 used as an adulterant in cheap paints. 



The commercial value of gypsum depends mainly on accessibility to 

 market. In 1899 the ground material was quoted at $2.00 a ton in 

 New York. In Michigan the average price of crude material has 

 been some $1.25 a ton, and for calcined plaster (plaster of paris) $3.00 

 to $5.00 a ton. 



3. Celestite. 



Composition sulphate of strontium SrSO^,= sulphur trioxide, 43.6 

 per cent; strontia, 56.4 per cent. Hardness, 3 to 3.5; specific gravity, 

 3.99; color, white, often bluish, transparent to translucent. Differs 

 from the carbonate (strontianite) b}' being insoluble in acids, but gives 

 the characteristic red color to the blowpipe flame. 



According to Dana the mineral occurs usually associated with lime- 

 stones or sandstones of Silurian or Devonian, Jurassic, and other 

 geological formations, occasionally with metalliferous ores. It also 

 occurs in beds of rock salt, gypsum, and clay, and is abundantly asso- 

 ciated with the sulphur deposits of Sicily. (Specimen No. 6087T, 

 U.S.N.M.) The principal localities in the United States are in the 

 limestones of Drummond Island, Lake Huron; Put in Bay, Lake Erie 

 (Specimen No. 53094, U.S.N.M.); Kingston, Ontario, in crystalline 



^See Mineral Statistics of Michigan, 1881, for details of plaster work of that State. 



