TABLE VIII. 
Color and 
amount of 
refraction. 
Colorless, 
white, red 
dish, green 
black 
through 
numerous 
inclusions 
not trans 
parent , as 
nepheline 
n— 1*657 
Colorless, 
sky blue, 
spotted, al- 
so brown 
through in 
elusions. 
Stands out 
well in sec- 
tions be- 
ing strong- 
ly refract- 
ive. 
*1=1.768 
£=1.760 
Chiefly 
bluish 
gray, 
brown. 
w= 1 . 64 
£=1.62 
Pleochro- 
ism. 
If colored, 
with evi- 
dent di- 
chroism. 
When col- 
ored, very 
strong 
(<i=sky 
blue 
£=.sea 
green. 
Structure. 
In irregular 
grains or long 
often slender 
columns, fre- 
quently , bro 
ken into joints 
by basal frac 
ture. Inclu 
sions. Only as 
accessory com 
ponent. As in 
elusions par 
ticularly fre 
quent in bisil 
icates, horn 
blende and 
biotite. 
Surface of sec 
tions rough. 
In round 
grains or short 
columns. Zo 
nary struct’re, 
blue nucleus 
and colorless 
cortical layer. 
Association 
Known to oc- 
cur in nearly 
all rocks. 
Inclusions. 
Iron black 
with me 
tallic lus 
tre. In 
thin plates 
blood red, 
also yel- 
lowish red 
and brown 
violet. 
Very 
strong di 
chroism. 
w=dark 
blue, 
brown to 
black. ^ 
£=light 
blue to 
brown. 
Macroscopic 
and very 77 ii 
nute crystals, 
rarely in 
grains, as in 
certain meta 
morphic rocks 
In granites co- 
alesced with 
quartz in 
grains Large 
individuals of- 
ten frayed out 
in a radiating 
manner at the 
end. 
Only in 
plates in crev- 
ices of miner 
als by infiltra- 
tion. Second- 
ary except per 
haps in ba- 
salts. 
With quartz, 
orthoclase and 
biotite, Pleon- 
ast, and anda^ 
lusite. 
Glass inclu- 
sions, gas 
pores Very 
characteris 
tic are black 
or brown 
needles, or 
minute 
grains filling 
the entire 
crystal, giv 
ing the cross 
section par- 
ticularly a 
remblance 
to hauyns. 
Central in 
elusion of 
glass etc. of- 
ten assum- 
ing the 
shape of the 
crystal. 
With ortho- 
clase and mus- 
covite in gran- 
ite. With 
quartz, ortho- 
clase, mica 
and other ac- 
cessory miner- 
als, such as 
staurolite and 
garnet. 
Very poor, 
fluid and 
glass inclu- 
sions; zir- 
I con; dusty 
brown inclu- 
. sions (in 
j “common 
corun- 
dum.”) 
In nearly all 
rocks particu- 
larly with de- 
composed bio- 
tite, horn- 
blende, au- 
gite, magne- 
tite, of which 
it is a product 
of decomposi- 
tion. 
A Iter a- 
tions. 
Al- 
ways 
un- 
chang 
ed. 
Occm'rence. 
Accessory in 
I nearly all 
jrocks. One of 
'the first min 
lerals to sepa- 
rate from the 
’magma. 
Very rare. 
Contact min’ 
jeral in meta- 
morphic slates 
and trachytic 
ejections. 
Very poor. 
Fluid inclu- 
sions. 
Into 
pulver- 
ent li- 
monite 
Remarks. 
Distinguish- 
able from 
hauyn in the 
longitudinal 
section and 
basal fracture; 
from olivine 
by optical pe- 
culiarities and 
fracture. 
If granular; 
similar to ap 
atite yet rec- 
ognized by 
colors of po- 
larization. 
Primary com 
ponent, fre- 
quent. Gran 
ular, accessory 
in many crys- 
talline slates 
and in clastic 
rocks. Char, 
acteristic in 
contact with 
eruptive rocks 
(See under as- 
sociation ) 
Easily recog- 
nized by crys- 
tal form and 
plcochroism. 
Distinguished 
from horn- 
blende by op- 
tical charac- 
ters. 
Easily recog- 
nized. 
