THE MINEKALS OF IDAHO 391 



CHRYSOCOLLA (504) 



Hydrous copper silicate, Crvptocrystalline. 



CuO.Si0 2 .2H 2 0. 



Chrysocolla, a mineral requiring further study to determine 

 its exact chemical and mineralogical nature, is an abundant and 

 important copper ore mineral in Idaho. The mineral varies from 

 blue, through various shades of blue-green and green and then to 

 browns, shading into what is described below as copper-pitch ore. It 

 is usually waxy in luster and appearance and massive or botryoidal on 

 free surfaces. Upon microscopic examination the mineral is ordina- 

 rily found to be crystalline and birefracting with definite optical 

 properties, but the optical properties vary widely in specimens from 

 different localities. An amorphous and isotropic copper silicate 

 corresponding to chrysocolla has been called cornuite. Chrysocolla 

 frequently resembles malachite, especially when present only as 

 a stain and, of the two green copper minerals chrysocolla is the more 

 abundant in Idaho. The principal occurrences of the silicate in 

 this state are as follows : 



ADAMS COUNTY 



Chrysocolla is first in order of importance among the oxidized 

 copper ore minerals in the contact-metamorphic copper deposits 

 of the Seven Devils district, and is very abundant in many places, 

 especially in the Arkansas mine. In fact the mineral is forming 

 to-day from drippings in many places in the abandoned workings. 

 It is intimately associated in places with copper pitch ore. 2 The 

 chrysocolla appears in masses of opaline texture associated with 

 malachite and in small veinlets cutting the other vein minerals 

 and penetrating all the interstices. Thin waxy green crusts of 

 chrysocolla result from the alteration of bornite and often encrust 

 masses of bornite (Cat. Nos. 51871, and 67391 U.S.N.M.). Speci- 

 mens from the Arkansas mine are pure and green of various shades, 

 the structure being massive or small botryoidal. Chrysocolla appears 

 abundantly in ore from Peacock dump and is waxy, translucent, 

 and various shades of pale blue-green, sea-green, sky-blue, etc. 



CUSTER COUNTY 



Although copper silicates are the most important constituents of 

 the oxidized ores of the mines about Mackay in the Alder ('reek 

 district, the silicate ore is characteristically brown in color with 

 vitreous to dull luster and is further discussed under copper-pitch 

 below. Locally the silicate is chrysocolla which is bluish green with 

 a vitreous luster. 



Specimens from the Tiger claim contain translucent emerald-green 

 to blue-green or blue chrysocolla with fluorite. Other specimens 



8 D. C. Livingston and F. B. Lanoy. Idaho Bur. Mines and Geol., Bull. 1, p. G7, 1029. 



