THE MINERALS OF IDAHO 279 



The ratio of ferrous iron to magnesia determines the position of 

 the pyroxene in the diopside-hedenbergite series. The metasilicates 

 of iron and magnesia are present in the above analysis in the molec- 

 ular proportion of Fe:Mg = 93:285 or 1:3.06, so that the material 

 may be designated diopside. 



A specimen of low-grade molybdenum ore sent to the National 

 Museum from Challis consists almost entirely of granular green 

 diopside containing flakes of molybdenite. Another specimen sent 

 in by J. W. Copper from Hill City, Custer County, consists in the 

 main of green diopsidic pyroxene. 



In the Copper Basin district at the head of East Fork of Big Lost 

 River diopside occurs abundantly in garnet-diopside zones in lime- 

 stone, which are mined for copper. 91 A specimen from the Parallel 

 tunnel of the Reed and Davidson mine in this district consists of 

 granular diopside, containing magnetite and copper silicates, in con- 

 siderable part altered to nontronite (chloropal). 



In the Washington Basin district diopside occurs with the ore of 

 the Empire ledge. In altered monzonite, in and adjacent to the 

 vein, feldspar and biotite crystals are completely transformed to 

 pyrrhotite and diopside. In the southern part of the vein pyrrhotite 

 with about an equal amount or intermixed quartz and diopside forms 

 a band 15 to 20 feet wide next to the hanging wall of the vein. 92 



LEMHI COUNTY 



Diopside has been noted as colorless granular material associated 

 with ludwigite in specimens from the Bruce Estate in the Texas 

 district. 93 It is probably common in this property, which is a low- 

 grade contact-metamorphic copper deposit in limestone. 



OWYHEE COUNTY 



Diopside occurs to some extent with other metamorphic minerals 

 in lime-silicate zones in limestone mined in the Golconda and other 

 mines in the South Mountain district. Specimens of lime-silicate 

 rock from the road on Williams Creek 2 miles below the mines, South 

 Mountain district, consist very largely of pale gray-green diopside in 



»i J. B. Umpleby. U. S. Geol. Survey, Prof. Paper 97, pp. 104-105, 1917. 

 « J. B. Umpleby. U. S. Geol. Survey, Bull. 580, pp. 245-246, 1915. 

 » 3 Earl V. Shannon. Proc. U. S. Nat. Museum, vol. 59, p. 667, 1921. 



