THE MINERALS OF IDAHO 



267 



of 8 acres, and a third of 2 acres. The hydromagnesite is from 2 to 4 

 feet thick, but below 2 feet the material is somewhat discolored. 80 A 

 specimen of typical material from the locality, furnished by Mr. 

 McDowell (Cat. No. 94140, U.S.N.M.) is white and earthy in texture 

 and somewhat friable. It is very similar in appearance to many 

 other white earthy materials and might be mistaken for chalk, clay, 

 diatomaceous earth, or tripoli. It is not plastic when moist. Under 

 the microscope the material appears mainly amorphous and iso- 

 tropic with a refractive index of about 1.54, but it contains very 

 numerous disseminated flakes of high birefringence which are too 

 minute for their properties to be determined. The mineral could 

 not be identified without chemical tests. An analysis of this material, 

 made by the writer in the laboratory of the National Museum, gave 

 the following results: 



Analysis of hydromagnesite from Soda Springs 



(E. V. Shannon, analyst) 



Per cent 



Insoluble (silica) 7. 52 



Alumina and ferric oxide ( AI2O3, Fe 2 3 ) 1. 77 



Magnesia (MgO) 38. 28 



Lime (CaO) 1. 18 



Carbon dioxide (C0 2 ) 34. 97 



Water (H 2 0) above 105° C 15. 41 



Water (H 2 0) below 105° C 1. 06 



Total 100. 19 



From the nature and occurrence of this earthy hydromagnesite it 

 would be expected to be impure. After deducting as impurities the 

 silica, insoluble matter, lime, iron, alumina, and water below 105° C, 

 the remaining constituents, recalculated to 100 per cent, are com- 

 pared with the theoretical composition of hydromagnesite below. 



These figures show that the sample consists of approximately 90 

 per cent of hydromagnesite with 10 per cent of various impurities. 

 These deposits may, in the future, have some commercial value for 

 refractory materials or the other uses to which magnesite is put. 

 The material is of a fair degree of purity and can be cheaply mined, 

 but the additional water which it contains would probably make it 

 more difficult and expensive to calcine than ordinary magnesite. 



80 Information furnished by J. Spotts McDowell, of the Harbison-Walker Refractories Co. Personal 

 letter, Nov. 13, 1920. 



