2(U 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. 
[NO. 228. 
Rocks G to M also collected by Spurr, but descriptions hitherto 
unpublished. Analyses L M, by W. F. Hillebrand, record No. 2087; 
the others by George Steiger, No. 2088. 
G. Early andesite, hanging wall of vein, 300-foot level, Mizpah 
mine. A more advanced stage of quartz-muscovite alteration than F. 
H. Extreme stage of alteration of andesite to quartz and muscovite, 
west drift, Mizpah vein. Quartz, with much muscovite. 
I. Augite-biotite-andesite, Mizpah extension shaft. Contains phe- 
nocrysts of plagioclase and augite, with some alteration to calcite and 
serpentine. 
J. Pyroxene-biotite-andesite, completely decomposed, Montana- 
Tonopah .shaft. Feldspars entirely altered to calcite, sericite, and 
quartz. Biotite and hornblende altered to chlorite, calcite, quartz, 
sericite, siderite, and pyrite. 
K. Biotite-dacite, north side of Mount Brougher. Toscanose. Con- 
tains plagioclase, possibly orthoclase, biotite, and a glassy groundmass. 
L. Biotite-andesite, Halifax shaft. Harzose. Contains plagioclase, 
biotite, augite, and magnetite. 
M. Biotite-pyroxene-andesite, North Star shaft. Entirely altered. 
Feldspar altered to calcite. Pyrite, siderite, and rutile are present. 
Si0 2 . 
A1A 
Fe 2 :! 
FeO. 
MgO 
CaO . 
K 9 
H,0 above 105 ° . 
TiO, ... 
ZrO L , 
CO, 
so. 
76.25 
12.84 
.54 
.33 
.56 
.16 
.12 
3.20 
2.14 
3. 17 
.37 
none 
.12 
FeS, 
MO. 
MnO 
BaO. 
SrO . 
Li 2 
F ... 
99.80 
91.40 
4.31 
.77 
.11 
.18 
none 
.06 
1.68 
.46 
.98 
.07 
.02 
none 
.04 
none 
none 
.06 
.02 
trace 
100. 16 
43.00 
16. 49 
2. 86 
6.31 
6.19 
5.69 
.12 
.84 
3.00 
7.93 
.89 
4.19 
.36 
.08 
2. 55 
.07 
none 
100.57 
57.51 
16.55 
3.20 
2.02 
2.30 
6. 06 
2.76 
2.81 
1.45 
2.56 
.80 
1.91 
.30 
none 
.02 
17 
100. 42 
71.71 
14.00 
1.06 
.51 
.43 
2.25 
3.21 
4.41 
.44 
1.38 
.28 
trace 
.07 
.54 
none 
100. 29 
56. 26 
16.18 
5.56 
1. 17 
2.78 
5.07 
3. 25 
3.43 
2.07 
2.61 
.73 
trace? 
.62 
.32 
none 
.03 
trace 
.21 
.12 
.06 
trace 
100. 47 
51.64 
15.58 
.16 
.58 
2.79 
6.25 
.27 
2.46 
2.56 
4.43 
.73 
trace? 
4.24 
.31 
.03 
7.89 
none 
.21 
undet. 
trace 
(?) 
I 
100. 13 
