6 PROCEEDINGS OF THE NATIONAL MUSEUM, VOL, 62. 
Kdward L. Jones, jr., illustrating his work in this district. The 
opportunity was thus offered for determining the mineralogical iden- 
tity of the secondary arsenates which form the brilliant coatings. 
The ore consists, as has been detailed above, of porous white quartz 
containing disseminated sulphides, including pyrite, chalcopyrite, and 
arsenopyrite, the latter in steel gray orthorhombic crystals. There 
is also some black sphalerite and perhaps a little enargite in the ore. 
The pyrite is partly coated by the black mineral, probably sooty 
chalcocite, and the quartz is brilliantly colored by thin films of a 
blue-green mineral with lesser amounts of a yellow-green to yellow 
mineral and an emerald-green crystalline one. 
The most abundant of these, the blue-green mineral, has a vitreous 
to pearly luster and resembles tyrolite. It gave qualitative chemical 
reactions for copper and arsenic. At the request of the writer Mr. 
A. Rodolfo Martinez very kindly worked out the optical properties 
of this mineral, and by reference to Larsen’s tables‘ it was found to 
agree with the rare arsenate trichalcite, as shown by the following 
comparison: 
Comparison of optical properties of trichalcite. 
Pine Creek, Idaho (Martinez). Turginsk, Urals (Larsen). 
Color pale bluish-green. Color pale bluish-green. 
Nonpleochroic. Nonpleochroic. 
Biaxial. Biaxial. 
Sien negative (—). Sign negative (—). 
2V large. 2V large. 
= 5 a= 1,67 + 0.01. 
Bi osee B = 1.686 + 0.003. 
= : y = 1.698 + 0. 003. 
Birefringence medium low. Birefringence 0. 028 
X normal to plates. X normal to plates. 
There is no other known mineral containing copper and arsenic acid 
which approaches these properties and, while it is regrettable that the 
mineral is not available in quantity sufficient for analysis, its identity 
can be considered as established by these data. 
Upon examination of the specimen under a binocular microscope 
it was found that the mineral was in thin tabular crystals of hexag- 
onal aspect, and although these were very minute it was found pos- 
sible to measure two of them on the 2-circle goniometer. The basal 
pinacoid gave good signals, but the very narrow prismatic planes were 
more or less curved and irregular, yielding only approximate measure- 
ments, accurate perhaps to 1°. These indicated 60° angles for the 
prismatic zone, the mineral thus simulating hexagonal crystallographic 
‘Edward L. Jones, jr., A reconnaissance of the Pine Creek district, Idaho. U.S. Geol. Survey Bull. 
710(a), pp. 1-86, 1919. 
4Esper S. Larsen, jr.. Microscopie determination of the nonopaque minerals. U.S. Geol. Survey 
Bull. 679, pp. 144 and 263, 1921. 
