F, A. Genth’s Contributions to Mineralogy. 249 
of sesquioxyd of iron, some of which was certainly mechanically 
mixed with it. Dr. Owen found by his experiments 35 p.¢. 0 
sesquioxyd of iron—from which it appears that this substance 
exists in the mineral in variable quantities. This fact and the 
other that dilute ammonia extracts the molybdic acid easily and 
completely, leave very little doubt that the Nevada City mineral 
is a mechanical mixture of molybdine with limonite, although I 
will admit that no positive opinion can be formed about it, unless 
larger quantities of the pure mineral are subjected to repeated 
analyses, 
5. Albite, 
divergent structure, but only, where calcite predominated and 
could be removed by acid, crystals could be obtained. They 
were small and indistinct, showed however the common form or 
twins of the same. The following planes are noticed: be ok 
1,1’, Oand iz. I analyzed a specimen of the granular variety, 
freed from calcite y dilute chlorhydric acid, and found: 
_ By J. L. Smith’s method. 
Silicie acid, < = - 68:89 
Alumina, - Fe - - - 19°65 “eee 
Sesquioxyd of iro Soak : - O41 ee 
Lina a ee wag 
Soda, - - - - OW 0°53 
Potash, “ s ‘ é - trace trace 
Ignition, - . . ‘ : 0-21 soe 
10010 
b. A massive greyish white variety of albite, much resembling 
petrosilex and some kinds of jasper, from the Steele mine, Mont- 
Somery county, N. C., has been examined in my laboratory by 
Mr, J.P. Pépplein, who found it to contain: 
Silicic acid,  - ‘ s - 60-29 
—— - < - ie i - - ted 
squioxyd of iron, aa - - ee ely = : et te — 
Oxyd of manganese, ‘ 3 ya A a  , 
Magnesia, “ in a ‘ é sane ———— aca 
Lime, a “ 2 = alae meat ae a poo 
Peal ee 
Water, : : Br Cia STA - 120 
99°45 
For the determination of the alkalies, the albite, both from the 
le mine and California, were decomposed by fluohydric acid. 
SECOND SERIES, Vor. XXVIII, No. §3.—SEPT., 1859. 
32 
