192 F. A. Genith’s Contributions to Mineralogy. 
This whitneyite is compact, with an exceedingly fine-grained 
structure, (far more so than that from the Pewabic location, which 
is rather coarse grained,) and a reddish, greyish white color and 
no lustre on surfaces of fresh fracture. Scratching developes 
strong metallic lustre and a reddish white color, but it soon tar 
nishes. Probably owing to some porosity the sp. gr. was found 
to vary from 8-246 to 8-471 (at 21° C.), the hardness is a little 
below that of fluor. It is slightly malleable. Fracture subcon- 
choidal. The analysis of the purest pieces gave: 
I II. III. Theory. 
Arsenic, 10-92* 12-284 12-277 11°64 
eCopper, 87°64 87477 87-371 88°36 
Silver, 019 0°040 0°032 
98°75 99°801 99°680 
they have the composition of algodonite; a slight admixture of 
whitneyite generally gives the arsenic a little too low. I found: 
Z 1 Il. Il. Theory. 
Arsenic, - —- 15°30 15°56+ 16-72 16°50 
opper, - - 84-22 8410 82°35 83:50 
Silver, - - 0-32 0°34 0.30 — 
99°84 100-00 99°37 
8. For comparison. with the arsenids of copper from Lake 
Superior, Prof. 
ments 
copper 
silver, containing about 60 Pp c. of the latter metal. arnishes 
i 
easily, scratches fluor with difficulty. The sp. gr. of an appa 
ently pure piece at 95°C. was =7°603; fracture subconch' ia 
brittle. Associated with cuprite, malachite, barytes, etc. + 
analyses gave: ss 
I. II. ? 
Py Aime, 8 ras 16°94 1644 
Cippet, 6 <0 4 ous 8182. 82°33 geil 
MG ie he poste _ trace 
3 9928 99:27 egos 
"_* An accident in drying the precipitate of 2Mg0, NH,O, AsO,-+HO compel 
“hee. iMgO, AO, whe gives it always too low. 
a oe 
ps 
i 
Sead 
