524 AUSTIN F. ROGERS 



of the best-defined amorphous minerals and have found it neces- 

 sary to introduce but two new names. In the future other new 

 names will be necessary, but their introduction will be gradual. 

 It is not desirable to recognize all amorphous mineral substances, 

 but only those that will stand the test of a critical examination, and 

 usually only those that are found in a number of localities. I 

 would emphasize especially the recognition of those with crystalline 

 equivalents, for then we have a comparison of properties which are 

 especially useful in determination. 



SOME OF THE PROMINENT AMORPHOUS MINERALS 



I now propose to describe and discuss what seem to be the 

 better established amorphous minerals, with especial emphasis 

 upon those that I have been able to study in more or less detail. 



Amorphous carbon (schungite, mineral charcoal). — Graphite is 

 the hexagonal modification of carbon, and the so-called amorphous 

 graphite is probably compact, dense graphite in a fine state of 

 division. Graphitite and graphitoid, according to Weinschenk, 1 

 are simply varieties of graphite. 



Schungite, described by Iostranzeff from near Schunga, 

 Government Olenez, Russia, is an amorphous modification of 

 carbon, for when treated with a mixture of potassium chlorate and 

 nitric acid it is soluble and is not, like graphite, converted into the 

 yellow, scaly substance called graphitic acid. 



Amorphous sulfur (sulfurite). — Besides the common ortho- 

 rhombic, and the rare monoclinic, sulfur found at a few localities 

 amorphous sulfur also probably occurs in nature. Rinne 2 has pro- 

 posed the name sulfurite for naturally occurring amorphous sulfur. 

 He describes an arsenical variety (arsensulfurite) which occurs as 

 amorphous crusts on andesite. 



Xanthochroite CdS(H 2 0) i . ? (greenockite in part). — -The cad- 

 mium sulfid which occurs as a thin incrustation on sphalerite is 

 amorphous, as has been recognized by Lacroix and by Christo- 

 manos. It is usually called greenockite, but the original cadmium 

 sulfid first described from Scotland and found in but few other 



1 Zeit.f. Kryst. u. Mi?i., XXVIII (1897), 291. 



2 Centralblattf. Min. Geol. u. Pal., 1902, p. 499. 



