a 
e 
W. F. Hillebrand—Calaverite from Colorado. 131 
oxidation to a great extent whereby the silver has become more 
evenly distributed throughout the ore. 
Professor Penfield has kindly contributed the following 
notes on the crystallography of the mineral : 
“The crystals of calaverite which were examined were 
developed with prismatic habit, but the prismatic zone was 
striated to such an extent that it was impossible to identify a 
single face in the zone, and on the reflecting goniorneter almost 
an unbroken band of signals was obtained in a revolution of 
360°. Owing to oscillatory combinations the crystals were 
also much distorted, so that they did not present regular cross 
sections. 
The prisms were attached so that doubly terminated ones 
were not observed, while the faces at the free end were small 
and developed with so little symmetry that after a study of a 
number of crystals it was found impossible to determine with 
certainty the system of crystallization. 
The crystals do not exhibit the perfect cleavage ascribed to 
sylvanite and krennerite, but are similar to the former in some 
of their angles. When placed in position to show their rela- 
tion to sylvanite they have their prismatic development paral- 
lel to the 6 axis. One erystal, which owing to its development 
was more carefully measured than any of the others, was 
apparently a twin about 101, and showed at the end the forms 
111 and 110. The measurements compared with the corre- 
sponding ones of sylvanite are as follows: 
Sylvanite. 
~ 111A (111) over twinning plane 93° 35’ 94° 30’ 
110, (110) “ « be BEND 34 43 
110A 111 36 35 Sel 
110A 111 in twin crystal 36 33 37)" 3 
Other forms which were measured could not be referred to 
the sylvanite axes, and it seems probable from their develop- 
ment and lack of symmetry that the erystals are triclinic; but 
no satisfaction was obtained after a long and careful study of 
the limited supply of material on hand. 
In conclusion, therefore, it may be stated that the crystals 
are probably triclinic, but near sylvanite in angles and axial 
ratio.” 
Laboratory of the U. S. Geological Survey, Washington, D. C., May, 1895. 
