1912] EaJde: The Minerals of Tonopah, Nevada 



17 



Turquois. — Small amounts of pale green turquois, fading 

 into white opaque masses, occur in the crevices of the Mizpah 

 vein at the 600-foot level. The mineral is associated with black 

 manganese oxides and kaolinite, and occurs in the vicinity of 

 much iodyrite. 



Pharmacosiderite. — The rare iron arsenate occurs as a coat- 

 ing on quartz at the 370-foot level of the Montana-Tonopah 

 mine. It is light yellowish green and occurs in distinct cubes, 

 with its tetrahedral symmetry indicated by diagonal striations. 

 A few crystals show small faces of the tetrahedron and narrow 

 faces of the rhombic dodecahedron. Deposited on this arsenate 

 are little botryoidal groups of an undetermined dark-red iron 

 phosphate with irridescent surfaces and light brown altered rims. 



Cacoxenite. — Radiating tufts of golden yellow and pale yellow 

 cacoxenite occur in the cellular quartz gangue of the Montana- 

 Tonopah mine, about the 500-foot level. The structure of the 

 minerals resembles burrs with short bristles, and the bristles or 

 needles often radiate from a central small circle like spokes from 

 the hub of a wheel. These bunches are typically deposited on 

 drusy quartz which is coated with brownish black velvety layers 

 of manganese oxide, or is colored brown or black by manganese. 



Sulphates : Gypsum, Jarosite, and Barite 



Gypsum. — Very little calcium sulphate is seen in association 

 with the specimens examined, and the mines were quite free of 

 calcium compounds which could form this common secondary 

 mineral. Some of the fissure walls are coated with thin layers 

 of colorless selenite, and it occasionally forms a glaze on argentite 

 and on some of the other secondary minerals. Brilliant crystal 

 faces are seen on the coatings but there are no well-defined 

 crystals. 



Jarosite. — The hydrous sulphate, jarosite, is the most prom- 

 inent of the secondary minerals precipitated from the solutions. 

 It is characteristic of the lower zone of oxidation and is in close 

 association with the larger part of the iodyrite. It generally 

 occurs in flaky masses and flaky coatings, varying from light 

 ochre-yellow to dark reddish brown. These flakes under the 

 microscope are seen to be basal plates with rhombohedral edges. 



