128 
CONTRIBUTIONS TO MINERALOGY. 
[BULL. '262. 
while the forms in the prism zone have as simple indices in one case 
as in another, as can be seen from the following- table. 
Dana. 
Gold- 
schmidt. 
010 
110 
120 
140 
010 ' 
210 
110 
120 
h 
I 
V 
Dana. 
520 
210 
111 
Gold- 
sehmidt. 
510 
410 
212 
8. PREHNITE. 
A mineral from Lower California, sent by G. F. Kunz for determi- 
nation, proved to be prehnite. The analysis gave the following, 
results: 
Si0 2 43. 48 
A1 2 3 24. 52 
FeA 34 
CaO 27. 19 
H.,0 4. 49 
100. 02 
Specific gravity 2. 90 
9. HORNBLENDE. 
Coating the walls and projecting into the amygdaloidal cavities of a 
lava from Mono County, Cal., were noted small crystals of hornblende, 
tridymite, and biotite. The locality of the rock, which was kindly 
furnished b>^ Mr. Maynard Bixby, of Salt Lake City, is given as 8 
miles west of Bridgeport, Mono County, Cal. The hornblende and 
tridymite occur in sharp crystals, of which a few were measured. 
Biotite occurs abundantly as small hexagonal plates, which, under the 
microscope, show at times a zonal banding in color, the darker being 
on the outside. The axial angle is very small — at times uniaxial. 
The hornblende occurs as long prismatic crystals, becoming extremely 
acicular and hairlike at times. It is often grouped in radiating bunches 
and again occurs in single prisms. Their maximum thickness is about 
one-half millimeter, and in length they reach not over 5 mm. Under 
the microscope the pleochroism is in shades of brown. The maximum 
extinction was 15°. 
