34 HILLEBRAND, MERWIN AND WRIGHT. [ApHi 25, 



always friable, some falling to powder. Gypsum frequently accom- 

 panies the metahewettite and often encloses it, producing then the 

 appearance of a distinctly crystallized red mineral. When pure the 

 powder is dark red ; gypsum present lightens the color. Even when 

 free from gypsum the red vanadate is almost always associated with 

 other minerals, partly residuals from the impregnated sandstone, 

 although occasionally almost pure material is found, like that repre- 

 sented by analysis II (p. 40). The impurities interfered greatly 

 at first with the precise determination of the composition of the van- 

 adate, particularly as to its water content. For this reason no quan- 

 titative analysis of the mineral from Paradox Valley is given, 

 although an abundance of the ore was at our disposal and one or 

 more analyses of it were made before purer material, from Thomp- 

 son's, in eastern Utah, was obtained. These analyses made evident, 

 however, the chemical identity of the Paradox and Thompson's 

 minerals. 



The ore at our disposal from Thompson's differs somewhat from 

 that of Paradox Valley by a greater variation in its shades of red, 

 some of these being very bright in contrast with the usually duller 

 shades of the ore from Paradox.^ There are also associated with it 

 at least two interesting minerals, both of which were also noticed 

 later in ore from Paradox and the Henry Mountains. 



One of these, gray in color, is a hydrous silicate of aluminum, 

 trivalent vanadium and potassium. It is no doubt the same silicate 

 that was first noted by one of us (H.) in carnotite ores and seems 

 to be a constant associate of all the uranium and vanadium ores of 

 western Colorado and eastern Utah, in some places constituting the 

 chief vanadiferous component of the ore. In the ore from Thompson's 

 it forms soft patches throughout the red mass, some of which are of 

 sufficient size to permit of separation in a fairly pure state.® Per- 



^ Ores of deep color have been found recently by Mr. Frank L. Hess, 

 of the U. S. Geological Survey, in the Henry Mountains, Utah. 



^ The gray mineral accompanying metahewettite occurs in firm granules 

 consisting of aggregates of very minute doubly refracting particles which 

 cannot be isolated for microscopic study. The refractive indices of aggre- 

 gates from various portions of the ore varied between 1.59 and 1.64, appar- 

 ently indicating differences in composition. Some larger lath-shaped particles 



