74 
CONTRIBUTIONS TO CHEMISTRY AND MINERALOGY. [bull. 167. 
after throwing oat the Ti0 2 and the water lost below 280° as extraneous, we get the 
following comparison between the results found and the theoretical composition: 
Si0 2 
TiO* 
V*0 3 
A1 2 3 
MgO 
FeO 
K,0 '.. 
H,0, 280°— 
H,O,280°-f 
Found. ' Reduced. Calculated, 
45.17 
.78 
24.01 
11.54 
1.64 
1.60 
10.37 
.57 
4.12 
99.80 
45.88 
45.52 
24.39 
11.73 
1.66 
1.63 
10.53 
4.18 
24.64 
11.62 
1.72 
1.55 
10.81 
4.14 
100.00 
100. 00 
This comparison, based on the ratio 21 : 22 : 159, is as satisfactory as could be 
expected. 
Of these component molecules the first represents the normal phlogopite type, 
the second is a trisilicate alkaline biotite, and the third, which forms 74.5 per cent 
of the whole mass, is a muscovite in which two-thirds of tho aluminum have been 
replaced by vanadium— in short, a vanadium muscovite. Ordinary muscovite is 
Al a (Si0 4 )3KH 2 , and whether a corresponding V3(Si04) 3 KH2 exists can be determined 
only by analyses of roscoelite from other localities, and so learning its range of 
variation. That vanadium may replace aluminum is shown by the fact that Piccini 
has prepared true vanadium alums. That roscoelite is essentially a vanadium mus- 
covite seems to be fairly well established. As for the molecule Al 2 (Si:308)3K 2 H4, its 
existence is indicated in some other micas, and in Simmler's "helvetan" it seems to 
be the dominant molecule. 
Note. — A full discussion of the mode of occurrence of roscoelite, with 
historical data relative to the species, is given by Mr. H. W. Turner in 
the American Journal of Science, 4th series, Vol. VII, June, 1899, p. 455. 
10. Mariposite. 
Samples of the peculiar micaceous mineral named mariposite by 
Silliman were collected at the Josephine mine, Bear Valley, Mariposa 
County, California, by H. W. Turner in 1894. } According to Turner it 
resembles talc optically, but chemically it appears to be one of the ill 
denned substances known, for want of a more precise name, as pinite. 
Two varieties were analyzed — one white, the other green, but neither 
analysis leads to any definite formula. The data are as follows: 
1 Occurrence described by Turner in Am. Jour. Sci., 3d series, Vol. XLIX, 1895, p. 377. 
