118 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
replacement ores. It is usually in the form of ill-defined crystals on quartz crusts, 
more rarely on fluorite or dolomite crusts. Fine crystals were obtained from the 
Conundrum mine, where they occur in vugs with fluorite in gneiss. Silver-white, 
thin, and bladed crystals, often showing radial arrangement, were found on joint 
cracks in the breccia of the Captain stopes of the Portland mine. Sometimes the 
crystals are contained in crystalline comb quartz (El Paso, C. Iv. & N., and Gold 
Dollar mines), or in chalcedony (Last Dollar mine). 
OXIDIZED TELLURIUM COMPOUNDS. 
The presence of oxidized compounds containing tellurium was first proved 
by Dr. R. Pearce. a In the same year F. C. Knight analyzed a light-brown, brittle 
substance, with bright-yellow streak occurring mixed with a metallic telluride, and 
found that, subtracting the telluride, it gave the composition under I and II. 
Analysis of tellurium compound from Cripple Creek. 
* 
I. 
II. 
III. 
30.27 
35. 44 
32.72 
Te0 2 . 
68.05 
62.79 
65. 45 
H 2 0. 
1.68 
1.77 
1.83 
100.00 
100.00 
100.00 
This would correspond to a ratio Fe 2 0 3 : TeO, : 11,0 = 2 : 4 :1 and to the formula 
2(Fe,0 3 , 2Te0 2 ) + H,0, requiring the composition given under III. No name was 
given to this compound, the homogeneity of which is, indeed, somewhat doubtful. 
Mr. Knight reports the presence of about a third of 1 per cent of selenium, 
but this element has not been discovered in any subsequent analyses of Cripple 
Creek ores. 
Two other tellurites have been described. The first is emmonsite, discovered 
by Hillebrand in a specimen from near Tombstone, Ariz., and also essentially a 
hydrated ferric tellurite. The second is durdenite, found by Dana and Wells in 
specimens from Honduras. This is a greenish-yellow, massive substance containing 
TeO, 67.1, Fe 2 0 3 27.7, H,0 10.2. Ferrotellurite and magnolite (Genth) from Boul¬ 
der County, Colo., have, probably, the compositions FeTe0 4 and Hg,Te0 4 , but 
neither species is satisfactorily established. 
Emmonsite .—A small quantity of a yellowish green tellurite was collected at 
the W. P. H. mine, Cripple Creek, where it occurred in a very rich pocket of ore, 
together with native gold and partly oxidized calaverite. The vein cuts granite 
and schist near the contact with volcanic breccia, and the pocket occurred at a 
depth of 245 feet. A similar substance occurred with rusty gold in the Moose mine 
and is reported from the Deadwood mine. It is probably general^ present in the 
rich, partly oxidized ore, though it has usually escaped detection. Dr. W. F. Hille¬ 
brand has examined this substance carefully, with the results in the quotation 
below. 6 
a Proc. Colorado Sci. Soc., vol. 5, 1894-1896, pp. 66-71. 
b Hillebrand, W. F., Emmonsite (?) from a new locality: Am. Jour. Sci., 4th ser., vol. 18, December, 1904, pp. 433-434. 
