THE MINERALS OF IDAHO 459 



MIRABILITE (743) 

 GLAUBERS SALT 



Hydrous sodium sulphate, Na 2 O.S0 3 . 10 H 2 0. Monoclinic . 



Mirabilite or glaubers salt occurs in Owyhee County and adjacent 

 parts of Oregon as an efflorescence and mixed with niter, epsomite, 

 and other salts. 



OWYHEE COUNTY 



Sodium sulphate, probably in part in the form of mirabilite, occurs 

 mixed with other salts, including niter, sodium chloride, and magne- 

 sium sulphate, in soil at the foot of rhyolite cliffs along Jump Creek. 

 At the Claytonia saline claims on Jump Creek west of the Mc Cloud 

 ranch a 10-inch bed of coarse salts consists principally of mixed 

 glauberite and epsomite. 58 



GYPSUM (746) 



Hydrous calcium sulphate, CaO.S0 3 .2 H 2 0. Monoclinic. 



Gypsum occurs both in fine granular massive form, known as rock 

 gypsum or alabaster, and as clear colorless crystals or transparent 

 grains, the latter known as selenite. The mineral may usually be dis- 

 tinguished from other substances which it resembles by its softness. 

 It can be scratched with the finger nail. Rock gypsum is used to 

 make plaster of Paris which is the basis of all hard plasters. The fol- 

 lowing localities have been recorded in Idaho: 



ADAMS COUNTY 



Gypsum in the form of clean perfectly transparent selenite inti- 

 mately associated with massive bornite has been obtained from the 

 South Peacock mine in the Seven Devils district. 50 



BANNOCK COUNTY 



Gypsum occurs in the sulphur deposits 5 miles east of Soda Springs 

 as small crystals associated with native sulphur. 



BEAR LAKE COUNTY 



Gypsum has been prospected 3 miles east of Montpelier on the 

 south side of Montpelier Canyon. There is a prospect hole in the 

 SW. \i sec. 32, T. 12 S., R. 45 E., where a small body of gypsum lies 

 on and fdls cracks in limestone of Pennsylvanian age. 



The gypsum is fine grained, white, massive, and seemingly pure- 

 It is not well exposed but the bed is at least 4 feet thick. The lateral 

 extent was not determined. An analysis made in the laboratory of 



»> G. R. Mansfield. Nitrate deposits in Idaho and Oregon. U. S. Geol. Survey, Bull. 620, pp. 24, 30-31 , 

 1916. 

 I'D. C. Livingston and F. B. Laney. Idaho Bur. Mines and Geol., Bull. 1, p. 63, 1920. 



