bb. Optical axial plaiie || i-V ; perfect cleavage in 1=87°. 
Name. 
Chemical 
comp . and 
reactions. 
Specif. 
Gray. 
Cleavage. 
Unsual combi- 
nations of form 
of sections. 
Twins. 
Optical deter- 
minants. 
Double re- 
fraction. 
I . Mono- 
3 17- 
Perfect 
Rarely in 
Very fre- 
Optical axis 
Positive, 
clinic All- 
R Si Qg 
3-41 
I 
grains crys- 
quent. 
plane || i-i^. 
“ strong. 
^ite Group 
R=-Mg. 
tals I, i— i. i-i^. 
twinning 
acute bisectrix 
Extinction 
a. Common 
Ca, Fe, 
I and i-i. 0, 
plane i-i, 
in the ob- 
in sections 
and basalt 
and Fes 
3-34- 
_i,I=87°6' 
also in pol- 
tuse angle j 3 . 
II b per- 
ic augite. 
O3 AI2 O3 
3-38. 
Sections per 
ysinthetic 
h=hC 
pf^ndicu 
According 
pendicular to 
twins. 
The positive 
lar; in sec- 
to Tscher- 
c octagonal 
More rare- 
axial angle 
tions in- 
mak a 
with evident 
ly inter- 
enlarges with 
clined to 
mixture of 
prismatic 
penetrat- 
the amount of 
i-i^ C: c 
Ca Mg Si-2 
cleavage. 
ing twins 
iron in rhomb- 
becomes 
Og-j-Ca Fe 
Longitudinal 
in a plane 
ic augite. 
smaller 
Sis 
section dis- 
of — I-i or 
about 60°. 
until it 
Mg AI2 Si 
torted hexag 
1-2' . 
Sections | i-i 
reaches 0 
Og Scarce- 
onal, with 
and perpen- 
when par- 
ly attacked 
cleavage lines 
dicular to c 
allel to i-i 
by acids. 
parallel to i-i^ 
[show the dis 
In sections 
quadrangular 
'appearance of 
II i-F C: 
often rhomb- 
an optical 
c=39° 54° 
ic. 
axis in almost 
the middle of 
the field. 
a:a=22°. 
b. Dial- 
do 
3-23- 
1(87°), 
\ 
do i 
do 
do 
lage. 
3-34 
shelly 
fracture in 
1 
1 
i-i. 
i 
i 
c. Ompha- 
do 
3-3 
As in au- 
Only in 
cite. 
with more 
gite, frac- 
grains. 
rare 
do 
do 
AI2 O3 
d6 
ture less 
perfect 
than in di- 
allage. 
do 
do 
do 
do 
d. Diop- 
more CaO 
side. 
than MgO 
poor in 
Also in long 
AI-2 O3 
columns with 
transverse 
do 
do 
do 
Fracture 
fracture, 
in 0 be- 
usually not 
e. Salile. 
poor in 
3 - 2 - 
sides the 
terminated. 
iron. 
3 - 33 - 
above. 
Section as in 
augite. 
