320 F. A. Genth—Contributions to Mineralogy. 
the requisite amount of arsenic was therefore calculated for the 
cobalt found, and after deducting in analysis I, 2:09 p. c. of 
pole] and in II, 26°83 p.c., the following results were ob- 
ned: 
Lead Se 72 33°99 
Silver 2°4 2°81 
Bismuth 39°06 37.48 
Cobalt : 2°41 4°22 
Arsenic 2 3°07 5°37 
Sulphur. 15°59 15°64 
100°33 99°51 
The analysis I shows an admixture of 6°79 p. c. of cobaltine, 
and II of 11°88 p.c. Deducting these quantities the compo- 
sition is : 
ead 40°32 38°79 
Silver 2°65 e421 
Bisumth 41°76 42°77 
Sulphur 15°27 15°23 
100°00 100°00 
rresponding closely wit the formula 2Pb (Ag) S + BiS,, 
eve the following per centage: 
2Pb 
emg tS 4 41°65 
Bi 210 42°25 
5S ‘ 80 16°10 
| 497 100°00 
= white quartz. "One of the crystals showed prismatic 
es similar to those of aragonite. Longitudinally striated. 
‘he =— gave: 
Lead 54°82 
Silver. _ trace 
Tron, 0°42 
i _ Antimony 26°85 
_ Sulphur. 17°91 
100-00 
6. Tetrahedrite a Arizona.—An analysis of a “ fahlerz”- 
like mineral from the —- mine near Prescott, me sp 
