64 
CONTRIBUTIONS TO CHEMISTRY AND MINERALOGY. 
[bull. 187. 
formerly of the United States Geological Survey, gave almost the 
theoretical composition as shown below. Specific gravity at 26° C, 
4.76, uncorrected for impurities. 
An analysis of enargite collected by Mr. Tower in the Earns mine, at 
Butte, is also given. 
Analysis of covellite. 
Cu 
66.06 
33.87 
.14 = .30FeS 2 
.11 
100. 18 
s 
Fe 
Insol 
Ratio Cu:S as 1:1.01. 
Analysis of enargite. 
Cu 
48.67 
.33 
.10 
17.91 
1.76 
31.44 
.11 
Fe 
Zn 
As 
Sb 
S 
Insol 
100. 32 
5. Tysonite and Bastnasite. 
These minerals formed a single fine specimen half as large as the 
fist, without crystal faces, from Cheyenne Mountain, near Pikes Peak, 
Colorado. The bastnasite covered one side of the tysonite to the depth 
of an inch. The line of demarcation between the two minerals was 
sharp, but examination of their sections by Mr. H. W. Turner showed 
the tysonite to be permeated by stringers of bastnasite along numerous 
cracks and that occasional grains of the latter were embedded in the 
tysonite, which accounts for the C0 2 shown in the tysonite analysis. 
Attached to the tysonite at portions of its surface were other white and 
brownish alteration products derived from it, as shown by qualitative 
tests. The tysonite was evidently the remnant of a single large crystal, 
since, according to Mr. Turner, all parts had the same optical orienta- 
tion. Mr. Turner further found the optical properties of both minerals, 
so far as determinable, to agree with those given in Dana's Mineralogy, 
and the index of refraction of the bastnasite to be greater than that 
of the tysonite. He likewise noted in both minerals minute colored 
inclusions, indeterminable and very trilling in amount, and also in the 
tysonite " numerous minute angular cavities in which there is a liquid, 
