A REVIEW OF THE AMORPHOUS MINERALS $37 



Hilgard 1 has recently described, from a locality near the City 

 of Mexico, a peculiar clay which consists largely of a hydrous 

 magnesium silicate. This substance was named lucianite, but as it 

 is a colloidal substance with specific gravity of 2 . 25 and is soluble in 

 hydrochloric acid it is probably a synonym of stevensite. 



Cornuite. wCuO ■ wSi0 2 * {H 2 0) x (chrysocolla in part) . — In spe- 

 cimens of chrysocolla from a number of localities I have noted a 

 glassy, green or bluish-green copper silicate which is the amorphous 

 equivalent of chrysocolla. To this newly recognized mineral I 

 wish to apply the name cornuite in honor of the late Dr. Felix Cornu, 

 of Leoben, Austria, who was practically the first mineralogist to 

 make a sharp distinction between crystalline minerals and their 

 amorphous equivalents. 



I have found this mineral on specimens from Globe, Arizona; 

 Bisbee, Arizona; Ludwig, Nevada; Copper Mountain, Alaska, 

 and Collahuasi, Chile. It is usually optically isotropic with n 

 varying from 1.525 to 1.549, but sometimes has irregular, weak 

 double refraction and wavy extinction. It is associated with 

 crystalline chrysocolla and often appears in colloform bands within 

 layers of colloform chrysocolla. It is more readily soluble in 

 hydrochloric acid than chrysocolla and also somewhat softer. 



The best specimens of cornuite in my possession are from the 

 mine of the Alaska Consolidated Mining and Smelting Company at 

 Copper Mountain, Prince of Wales Island, Alaska. It occurs 

 as a beautiful bluish-green (Ridgway 42k), transparent, glassy, 

 somewhat banded crust about 1 cm. thick associated with chryso- 

 colla. The index of refraction is 1 . 549=^0. 001. I am indebted to 

 my collegue, Dr. G. S. Bohart of the chemistry department, for 

 the following analysis of the Copper Mountain cornuite: 



Ratios 

 CuO =42.61 O- 537 



A1 2 3 = 0.31 ..0.004 



Si0 2 =34-13 0.566 



H 2 = 23 . 1 1 1 . 284 



These figures are each the average of two closely agreeing values 

 made upon carefully selected material free from the associated 



1 Proc. Nat. Acad. Sci., II (1916), 8-12. 



