The Ameficafi Geolosdst. 
August, 1898 
with the aiigitcs and olivines. The structure and niineral com- 
])osition places the rock at once among the diabases, and on 
account of the large amount of olivine it is definitely classed 
as an olivine diabase. 
The Aiigite occurs in large crystals with indistinct crystal 
outline. Sections cut parallel to the plane of symmetry show 
a very perfect cleavage. The pleochroism of some sections 
is fairly strong. a=reddish-brown, b^^pale greenish-yellow, 
C:=:blue-green. Maximum extinction angle measured against 
the prismatic cleavage c^ ^=47°. Inclusions of magnetite are 
common in the augite crystals. The augite was separated 
from the other minerals by means of Thoulet's heavy solution 
and further by a magnet and lens to obtain particles as free 
from magnetite inclusions as possible. These were analyzed 
with the following results. (See i in table). 
Table No. 2. 
Analysis of Aiigite. 
CONSTITUENTS. 
I 
II 
III 
RATIO OF I 
Silica SiOo 
48.83 
4.41 
10.01 
20.51 
17. II 
48.80 
4.14 
12.36 
19.49 
14.33 
H2O0.88 
49-33 
9.15 
0.27 
FeO 9.05 
16.36 
14.58 
0.55 
0. 19 
Ign. 0.25 
.801 .801 
Alumina AlgOg 
.043 -043 
.125] 
.366^ ^'S 
• 427 J 
*Iron FcOg 
Lime CaO 
Magnesia MgO 
Soda Na.jO 
Potash K.,0 
Total 
Specific gravity 
100.87 
3-232 
99-73 
RO: R303:Si02=2i:i:i9 
I. Olivine diabase from near Chatham, Virginia. 
II. Analysis of an augite given by Hintze C. Handbuch der Mineral- 
ogie, 1893, II, p. 1 107, No. CXII. Quoted from Lemberg, Zeitschr. d. 
geol. Gesch. 1877, 29, 495. 
III. Analysis of diallagic augite in hypersthene diabase, from Cul- 
pepper county, Virginia. See Campbell & Brown, Bull., G. S. A., 1891, 
2, p. 344- 
The specific gravity of these fragments was 3.232. 
*A11 iron calculated as FegOg. Assuming it all to be in the form of 
FeO, the results then become 10.01 per cent. Feg03^=9 per cent, of FeO - 
giving a total of 99.86 per cent, for the analysis. 
