130 W. Ff. Hillebrand—Culaverite from Colorado. 
but it could not be detected in the amount of mineral taken 
for the above analyses. 
Excluding everything but gold, silver, and tellurium and 
recalculating to 100, the following comparison is obtained : 
Tis ratio. iit ratio. Tis ratio. 
Te 57°60 2°01 57°40 2°05: » 0 30 2°09 
Au 39°17 s 40°83 ; 41°80 f 
Ag 3-93 1:00 177 1-00 -90 1‘00 
100:00 100°00 100:00 
The ratio here obtaining is that for sylvanite and calaverite, 
but the very low percentage of silver shows that the mineral is 
calaverite. Indeed the first analysis agrees aimost exactly with 
Genth’s analyses of the species. Interesting is the slight varia- 
tion in the ratio between gold and silver, and the very low per- 
centage of silver in the mineral from the C. O. D. and Raven 
mines. Calaverite, the lowest silver carrier of the gold-silver 
tellurides, has not heretofore been known to carry less than 
three per cent of silver. 
The pyrognostic characteristics of the mineral from the 
Prince Albert mine were essentially those ascribed to calave- 
rite. In the closed tube it fuses, giving a white coating near 
the assay, and a globular gray coating just above, which latter 
by strong heat can bein part driven higher up, leaving the glass 
covered with the same white fused coating as lower down. 
This latter is yellow while hot. On charcoal the mineral fuses 
with a green flame, giving a white coating and similar fumes, 
and leaving a yellow bead. The color is pale bronze-yellow, 
in powder greenish gray. ‘The hardness is not less than and 
perhaps a little over 8. Specific gravity, as given above, 9-00. 
The identity of the telluride occurring at Cripple Creek, 
which in oxidizing gives free go'd and oxidized tellurium com- 
pounds* seems thus satisfactorily established, but unless there 
is another richer in silver the mode of occurrence of the silver 
in some of the ores is still in large part unaccounted for. It 
may be derived from a very rich argentiferous tetrahedrite of 
which Prof. Penrose submitted a small specimen for identifica- 
tion. This carries over eleven per cent of silver, but is said 
to be excessively scarce and therefore hardly to be considered 
in this connection, unless indeed this should have been the 
original source of most of the silver and later have suffered 
*From tests made by myself on a number of specimens collected by Prof. 
Penrose the combinatiun seems to be chiefly if not altogether with iron, but 
whether as tellurite or tellurate could not be ascertained. 
