46 Reéramination of American Minerals. 
16. Biotite of Puinam Co., N. Y, 
In appearance this mineral resembles talc, having a wavy, lam- 
ellar structure, and a soapy feel. Its color is brownish green in 
mass, and pale yellowish green by transmitted light. Hardness 
2-2°5. Sp. Gr. 2°80. The laminz are entirely devoid of elas- 
ticity. It has been called pyrophyllite by some mineral collec- 
tors, but upon what grounds we are ignorant, as it does not pos- 
sess the remarkable property of exfoliating and swelling up by 
heat, so peculiar to pyrophyllite. Analysis shows its composition 
to be identical with Biotite. 
‘ 2. 
Silica, ‘ > 39°62 : 5 89°49 
Alumi i 17:35 ; ‘. 17-06 
pomeape of i iron, : ‘40 ‘ : 521 
Magnesia, 23°85 23°65 
Potash, 8 prisons 
oda, 1-01 rahe BE 
Water, F , 1-41 ; a 
Fluorine, ; . 1:20 wee — 
Chlorine, : . 3] we 
99:06 
R 8 Si 
Analysis 1 gives oxygen ratio 11:22:9°73: 20-58, or 1:1: 
and the oe aA as for the mineral last mentioned, R Si+# Si 
The ens mined were received from Mr. Silas R. 
Horton, of Craigville, New Yor 
17. Margarodite. 
This mineral occurs at Lane’s Mine, Monroe, Conn. It has 
been analyzed by W. H. Brewer,* but owing to some. impurities 
in his Sagi he obtained an excess of silica. 
ens very carefully selected, to avoid the fluor spar, and 
other siiherils with which it is associated, gave: 
Ls 2. 
Silica, : : 46°50 3 : 45°70 
Alumina, ‘ ; 33°91 5 & 33°76 
Peroxyd of iron, : 2°69 : : 311 
Magnesia, i 90 . ‘ 115 
Potash, ; : 7-32 ; : 7-49 
: ‘ 2-70 ‘ 2°85 
Water, 4°63 490 
Fluorine, 82 é 82 
Chlorine, “31 31 
99-78 10009 
These correspond to the analysis of margarodite from St. 
Etienne, in which Delesse found, 
Si e Mg Na K ii FI 
4623 3308 3848 210 145 887 412  trace=99'33 
In a former paper we have mentioned the difficulty of obtain- 
ing a correct formula from the analyses of margarodite, owing to 
* Dana’s Mineralogy, 3d edit., p. 359. 
