figure is visible; durable refraction negathe. TABLE XI. 
bisectrix, in O negative. 
Color Cf 
refract. 
Structure. 
Association 
Inclusions 
Alterations 
Occurrence. 
Remarks. 
Colorless. 
flesh 
colored, 
relief 
strong. 
/ 3 p= 
1.63S 
Pleochi'o- 
ism. 
a=dark 
blood red 
h=oil 
green 
c=olive 
green. 
c>b>a. 
Rarely in 
grains, almost 
always colum- 
nar like stau- 
rolite. Often 
so full of in- 
clusions as to 
obscure the 
andalusite. 
Often in radi- 
ating aggre- 
gates of long 
needles. 
With 
quartz, 
orthoclase. 
biotite, 
muscovite. 
Sometimes 
poor, often 
as in met- 
amorphic 
slates, rich 
in quartz 
grains, 
bitumen 
and scales 
of biotite 
Often into 
greenish 
fibrous 
aggregates 
Primary ac- 
cessory in 
granite and 
cryst. slates, 
as metamor- 
ph. mineral in 
contact 
schists, etc. 
Distinguished from 
augite by pleochro- 
ism and perpendic- 
ular extinction; 
from enstatite by 
character of double 
refraction; from 
hypersthene by col- 
or and double re- 
fraction, from zoi- 
cite by pleochroism, 
form of sections 
etc.; more difficult 
to distinguish from 
sillimanite which, 
however, occurs in 
minute needles. 
Violet 
blue, col- 
orless in 
very thin 
sections. 
1.56 
a=yel- 
lowish 
white, 
16 = berlin 
blue. 
b>a>cC 
Never in 
microlites. In 
large round 
grains or small 
crystals (in 
eruptive 
rocks.) Amet- 
amorphic 
mineral. 
With 
quartz, or- 
thoclase, 
and biotite 
With 
quartz 
sanidine, 
pleonast, 
and corun- 
dum. 
Fluid in- 
clusions, 
sillimanite 
needles, 
pleonast 
crystals, 
zircon, 
gl-assy in- 
clusions. 
Very fre 
quent, par- 
ticularly 
when oc- 
curing in 
grains. 
Changes to 
a fibrous 
green ag- 
gregate re- 
sembling 
andalusite 
(pinite) . 
Rare, as ac 
cessory, pri- 
mary constit- 
uent of gran- 
ite, quartz^ — 
porphry 
(pinite) and 
in grains in 
gneiss. Rarely 
in Trachytes 
and trachytic 
volcanics. 
In thin sections 
much resembling 
quartz, but may be 
distinguished by the 
decomposition. 
bisectrix in 0 (negative.) 
Colorless- 
white. 
/?p=i.7o 
relief 
strong. 
The trans- 
verse fractures 
of the long 
columns is 
characteristic, 
also the inclu- 
sions. 
With 
quartz, 
ompha- 
cite,garnet 
mica, and 
horn- 
blende. 
Fluid in- 
clusions 
are nu- 
merous. 
Frequent- 
ly cloudy 
on the 
edges. 
Frequent in 
crystalline 
slates as 
eclogites and 
particularly 
amphibolites. 
Easily distinguish’d 
from apatite by op- 
tical peculiarities, 
from andalusite by 
cleavage in O , and 
the pleochroism and 
colors of polarizat’n. 
Never microlitic as 
Sillimanite. It dif- 
fers irom olivine in 
crystal form, etc . 
