THE MINERALS OF IDAHO 277 



Every gradation between these two end members is possible, and 

 isomorphons mixtures intermediate and near the 1 : 1 ratio are some- 

 times designated by the varietal name sahiite. Augite is similar to 

 the diopside series, but differs in containing a notable amount of 

 alumina. Members of the diopside-hedenbergite series commonly 

 occur as metamorphic minerals, especially in limestone, while augite 

 characteristically occurs as a rock making mineral on basic igneous 

 rocks. 



The approximate composition of a pyroxene of the diopside-heden- 

 bergite series may be determined from its refractive index. The 

 optical properties of the end members of the series are: 



Diopside 2V = 59° ZAf = 38^° 0= 1.671 Biref.=0.030 



Hedenbergite 2 V = 60° ZAc=48° j8= 1.737 Biref.= .019 



In the absence of chemical data the minerals of the series may be 

 allocated by the following approximate classification: 



Diopside /3 refractive index from 1.671 to 1.693. 



Sahiite /3 refractive index from 1.693 to 1.715. 



Hedenbergite /? refractive index from 1.715 to 1.737. 



Other less common members of the pyroxene group probably 



occur in Idaho, but in general little attention has heretofore been 



paid to the silicate minerals and few specimens have been collected 



for study. 



DIOPSIDE 



Calcium-magnesium silicate, Monoclinic. 



CaO.Mg0.2Si0 2 . 



The calcium-magnesium pyroxene, diopside, including members 

 of the diopside-hedenbergite series in which magnesia is notably 

 preponderant over iron, is by far the most common pyroxene in 

 Idaho. 



ADAMS COUNTY 



Diopside is listed by Livingston and Laney 8S as a mineral common 

 in the contact-metamorphic copper deposits of the Seven Devils 

 district, and it has been noted in many specimens from this district 

 by the writer. A specimen from the roadside near the lower tunnel 

 of the Queen mine consists principally of granular green diopside, 

 of the variety known as coccolite, with calcite, brown garnet, and 

 disseminated grains of chalcopyrite. 



BLAINE COUNTY 



In the Hailey quadrangle diopside forms large rock masses, prob- 

 ably derived from dolomitic marbles, in the crystalline rocks form- 

 ing the crest of the range. Such diopside rocks are well exposed in 

 the cirques of the west side of Mount Hyndman at the head of 



6 « D C. Livingston and F. B. Laney. Idaho Bur. Mines and Geol., Bull. 1, p. 62. 1920 



