1914-] HYDROUS CALCIUM VANADATES. 35 



haps the greenish tints of some of the Paradox ore specimens are 

 caused by this or another related silicate, like the roscoelite from 

 Placerville, Colorado.' 



The second characteristic mineral is selenium, in amount up to 

 one per cent, of the ore from Thompson's. It seems to be included 

 as specks in the gray silicate. It is entirely absent from the speci- 

 mens of Paradox ore first obtained, but is present in ore from the 

 Henry Mountains, Utah, and in some small specimens seen recently 

 that were said to come from Paradox Valley. The presence of sele- 

 nium can be detected by heating the ore in a glass tube closed at 

 one end, when a red sublimate (sometimes accompanied by a white one 

 of selenium dioxide) appears when most of the water has escaped. 

 The fact that the free element appears as a sublimate does not by 

 itself prove the existence of the selenium in the free state in the ore, 

 for there was enough organic matter present, in a state invisible to 

 the eye, to reduce an oxygenated compound of selenium if present. 

 But the weight of evidence points to its presence in the elemental 

 state and not as a selenide or oxygenated compound.^ No connection 

 was observed between the presence of the selenium and the bright 

 red color of some specimens of the ore. The differences in shades 

 of red are attributed to differences in physical condition of the 

 metahewettite and to the effect of associated minerals. 



were observed, possibly pseudomorphs, containing abundant dark inclusions 

 of more or less prismatic shape arranged parallel to the laths. These laths 

 are aggregates, but portions of them seem to have a definite orientation with 

 respect to the outlines, extinguishing parallel and having 7 parallel to their 

 lengths. The inclusions were selenium and bituminous matter. This gray 

 material is probably not roscoelite. For purpose of comparison a study was 

 made of the properties of the roscoelite from Placerville, California, prob- 

 ably identical with that previously analyzed by Hillebrand (Am. J. Sci., 7, 

 351, 1899; Bull. U. S. Geol. Survey, No. 167, p. 70, 1900). 



Optical properties of roscoelite: Color, deep green with almost metallic 

 luster. 2E variable between 60° and 75° or more. Optical character — . 

 7 = 1.68(^1.685, /3 = I.675-1.680. 



"^ Hillebrand and Ransome, Am. J. Sci., 10, 120, 1900, Bull. U. S. Geol. 

 Survey, No. 262, p. 18, 1905. 



8 The mineral presents deep red transparent prisms, up to 0.05 mm. long, 

 showing parallel extinction. This characterization fits one of the known 

 forms of selenium. Sublimation tests on a few specks indicated free sele- 

 nium. It seems to be insoluble in carbon bisulphide. So far as known this 

 is the first established occurrence of elemental selenium in nature. 



