A REVIEW OF THE AMORPHOUS MINERALS 525 



localities is hexagonal. A new name is necessary for amorphous 

 cadmium sulfid and I propose to call it xanthochroite (Greek xanthos, 

 yellow, chroa, color). 



This mineral has recently been found, near Topaz, Mono 

 County, California, where it occurs as a thin coating on massive 

 magnetite. With the magnetite is associated sphalerite, and the 

 xanthochroite is doubtless a secondary mineral derived from 

 sphalerite. It varies from yellow to orange in color and is almost 

 opaque when examined with the microscope. There is no evidence 

 of crystallization or double refraction. It is soluble in hydrochloric 

 acid and is reprecipitated by hydrogen sulfid. It is immediately 

 darkened by copper sulfate solution, and this will probably dis- 

 tinguish it from crystalline greenockite. 



Hydrotroilite. FeS(H 2 0)^. — The black slime found in inland 

 seas and in some moist sands and clays is colloidal and amorphous 

 ferrous sulfid. It has been described from Hadishibey Liman in 

 Southern Russia by Sidorenko 1 and the name hydrotroilite given to 

 it. As troilite is a synonym of pyrrhotite, the name is not a very 

 fortunate one, but it has priority. 



I am indebted to Mr. G. A. Waring, of the United States 

 Geological Survey, for a black slimy deposit from the Kruzgekampa 

 Spring, 60 miles north of Nome, Alaska. This consists of a black, 

 opaque substance mixed with sand grains and diatoms. The black 

 substance is hydrotroilite. It is soluble in cold hydrochloric acid 

 with the evolution of hydrogen sulfid. The solution gives tests for 

 ferrous iron, and with ammonia a black precipitate is obtained. 



Wherry 2 proposes to call the melnikowite of Doss 3 /c-pyrite, but 

 melnikowite is microcrystalline (metacolloidal) FeS 2 and not amor- 

 phous. This is a serious objection to Wherry's scheme of nomen- 

 clature. 



Opal. SiO^HjO)* (lardite). — Opal is a typical amorphous 

 hydrogel and is unique in that, until Cornu's work in 1909, it was 

 the only amorphous equivalent of a crystallized mineral generally 



1 For reference to original article see Nenes Jahrb.f. Min. Geol. u. Pal., II (1902), 

 ref. p. 397. 



2 Central, f. Min. Geol. u. Pal., 1913, p. 518. 



* Neues Jahrb., Beil. Bd. XXXIII (1912), 689-93. 



