416 REPORT OF NATIONAL MUSEUM, 1899. 



snow-white aggregates of small acioular crystals of a high degree of 

 purity. (Specimen No. 62088, U.S. KM.) The composition of the 

 natural salt is given as follows: 1 Insoluble residue, 0.08 per cent; 

 magnesium sulphate (containing traces of calcium and sodium sul- 

 phates), 51.22 per cent; water, 47.83 per cent; chloride of sodium, 

 calcium, and magnesium, 0.42 per cent; iron, trace; loss, 0.45. 



8. POLYHALITE. 9. KAINITE. 10. KlESERITE. 



For description of these minerals see under Halite, p. 195. 

 11. ALUMS. 



Under this head are included a variety of minerals consisting essen- 

 tially of hydrous sulphates of aluminum or iron, with or without the 

 alkalies, and which are not always readily distinguished from one 

 another but by quantitative analyses. The principal varieties are kalin- 

 ite, tschermigite, mendozite, pickeringite, apjohnite, halotrichite, and 

 alunogen. Aluminite and alunite are closely related chemical com- 

 pounds, but differ in hardness and general physical qualities and in being 

 insoluble except in acids. 



Although possible sources of alum, none of these minerals have been 

 to any extent utilized in the United States, owing to a lack of quan- 

 tity or inaccessibility, the main source of the alum of commerce being 

 cryolite, bauxite, and clay, as elsewhere noted. (See pp. 214, 229, 

 and 325.) 



KALINITE is a native potash alum; composition K 2 SO 4 .A1 2 (SOJ 3 + 

 24H 2 O,= sulphur trioxide, 33.7 per cent; alumina, 10.8 per cent; potash, 

 9.9 per cent; water,45.6 per cent, or, otherwise expressed, potassium sul- 

 phate, 18.1 per cent; aluminum sulphate, 36.3 percent; water, 45. 6 per 

 cent. Hardness, 2 to 2.5; specific gravity, 1.75. This in its pure state 

 is a colorless or white transparent mineral, crystallizing in the isometric 

 system, readily soluble in water, and characterized by a strong astrin- 

 gent taste. In nature it occurs as a volcanic sublimation product, or 

 as a secondary mineral due to the reaction of sulphuric acid set free by 

 decomposing iron pyrites upon aluminous shales. Its common mode 

 of occurrence is therefore in volcanic vents (Specimen No. 60685, 

 U.S.N.M., from Vulcano) or as an efflorescence upon pyritiferous and 

 aluminous rocks. Being so readily soluble, it is to be found in appreci- 

 able amounts in humid regions only where protected from the rains, as 

 in caves and other sheltered places. So far as known to the author, the 

 mineral is nowhere found native in such quantities as to have any great 

 commercial value. 



TSCHERMIGITE is an ammonia alum of the composition (NHJ 2 SO r A1 2 

 (SO J 3 +24H 2 O, = aluminum sulphate, 37.7 per cent; ammonium sul- 

 phate, 14.6 per cent; water, 47.7 per cent. So far as reported this salt 

 has been found only at Tschermig and in a mine near Dux, Bohemia. 



1 Bulletin No. 14, October, 1893, Wyoming Experiment Station. 



