ON CARNOTITE AND ASSOCIATED VANADIFEROUS MINERALS 
IN WESTERN COLORADO. 
By W. F. Hillebrand and F. L. Kan some. 
INTRODUCTION. 
By W. F. Hillebrand. 
The rather widespread occurrence in western Colorado of consider- 
able quantities of a canary-yellow ore of uranium has been known for 
a few years past. It has been marketed to the extent of a few tons, 
but its mineralogical nature was unknown or incorrectly surmised 
until 1899. 
In the spring of that year a specimen of this ore first reached my 
hands through Dr. George P. Merrill, of the United States National 
Museum, and y, as soon found to contain a mineral or minerals new to 
science. Within a week appeared the announcement by MM. C. Friedel 
and E. Cumenge" of a new mineral, carnotite, a hydrous vanadate of 
uranium and potassium, obtained through Mr. Poulot of Denver, from 
Roc Creek, Montrose County, Colo. Mr. Poulot had already identi- 
fied vanadium in it. It was at once seen, despite certain differences 
in composition, that the two were identical. 
According to the French authors the mineral is of simple composi- 
tion, as above expressed, with only a little iron and mere traces of 
Al, Ba, Cu, Pb, and also, according to M. and Mme. Curie, of the 
radio-active substances radium and polonium. The empirical formula 
2U.,0 ;{ , V 2 5 , K 8 0, 3H a O, was assigned to it, some doubt attaching to 
the, water. 
Since then I have been able to examine carnotite from several local- 
ities in western Colorado, finding in each case the same lack of agree- 
ment with the anatyses of Friedel and Cumenge. 
While I was engaged in this work my attention was called to certain 
more or less greenish sandstones from the vicinity of Placerv 7 ille on 
the San Miguel River, San Miguel County, Colo., which were said to 
be highly vanadiferous and of considerable extent, and in which a zone 
a Bull. Soc. Chim. de Paris (3), xxi, 328, 1899; Bull. Soc. Franc. Min., xxii, 26, 1899; Comptes Rendus, 
:xxviii, 532, 1899; Chemical News, lxxx, 16, 1899. The papers as published in French differ slightly. 
