144 Hillebrand and Ransom e — Minerals in Western Colorado. 



to the same conclusion as in the case of the green cementing 

 material of the Placerville sandstone. The phengite-muscovite 

 ratio of that is not apparent here. Yet it is not at all unlikely 

 that a mineral like the one from Placerville is present, but 

 contaminated with some other. In fact it would be surprising 

 to find in such thoroughly altered sandstones anything but a 

 mixture. The fact of the existence of such vanadiferous tran- 

 sition products is itself highly interesting, and these tedious 

 analyses cannot therefore be considered as made in vain. The 

 mud-like amorphous character of this material precludes any 

 hope of aid from the microscope in solving the question of its 

 homogeneity. 



Summary. 



The body called carnotite is probably a mixture of minerals 

 of which analysis fails to reveal the exact nature. Instead of 

 being the pure uranyl-potassium vanadate, it is to a large 

 extent made up of calcium and barium compounds. Intimately 

 mixed with and entirely obscured by it is an amorphous sub- 

 stance — a silicate or mixture of silicates — containing vanadium 

 in the trivalent state, probably replacing aluminum. 



The deposits of carnotite, though distributed over a wide 

 area of country, are, for the most part, if not altogether, very 

 superficial in character and of recent origin. 



The green coloring and cementing material of certain sand- 

 stones near Placerville, Col., is a crypto crystalline alumino- 

 vanadio-potassium silicate resembling roscoelite, but with the 

 percentage proportions of Al 2 O s and Y 2 3 reversed. It consti- 

 tutes over 25 per cent of the sandstone at times, and contains 

 nearly 13 per cent of V 2 3 , the latter amounting in the maxi- 

 mum case observed to 3'5 per cent of the sandstone. 



As yet these highly vanadiferous sandstones have been found 

 only at Placerville, where it is intended to work them for 

 vanadium. Carnotite is associated with them in only trifling 

 amount. 



Other sandstones noticed owe their bright green color to 

 chromium. In yet another case where the color was dull 

 green, this was not due to either chromium or vanadium. 



TJ. S. Geological Survey, April, 1900. 



