TABLE X. 
Colors 
ofpolar- 
izatioii. 
Color 
and Re- 
fraction. 
Striiclure. 
Associa- 
tion. 
Inclusions. 
Altej'a- 
tlons. 
Occurrence. 
Remarks. 
In ter - 
ferance 
colors 
not 
nearly 
as bril- 
liant as 
in mon- 
oclinic 
augite. 
1.639 
Dark 
brown. 
Slight 
pleochroism 
Partly in 
large ir- 
regular 
grains in 
coarsely 
granular 
rocks part- 
ly in sharp- 
ly defined 
crystals in 
porphyrit- 
ic erup- 
tives. 
\ 
With 
olivine, 
plagio- 
clase, 
mono • 
clinic 
augite, 
magne- 
tite. as 
enstatite 
Inclusions ot 
brown rect- 
angular plates 
or opaque 
needles paral- 
lel to i-i. 
\ 
Into a 
1 green 
fibrous 
i aggre- 
gate as 
basite 
with sep- 
aration of 
Fe.^ or 
Fe; 0, . 
As enstatite. 
01 ten replac- 
ing nionoclin- 
ic augite as es- 
sential. Also 
in later basic 
eruptives and 
coarsely gran- 
ular older 
rocks. 
Distinguished 
from augite 
only by study 
of transverse 
section and 
perpendicular 
extinction in 
longit. sec- 
tions from 
hypersthene 
by pleochro- 
ism and d’ble, 
refract., from 
hornblende 
and biotite by 
absence of 
strong pleo- 
chroism. 
Bril- 
i liant. 
Dark brown 
/ 3 p=i. 636 , 
relief faint 
strongly 
pleocroic. 
Parallel to 
c greenish 
yellow, at 
right angles 
reddish 
brown. 
Inclusions 
as in 
bronzite, 
longit sec- 
tions seem- 
ing fibrous 
on account 
of cleav- 
age. 
With 
olivine, 
plagio- , 
clase, 
augite, 
and 
horn- 
blende. 
Minute brown 
and green 
regularly ar- 
ranged scales 
like mica. 
Otherwise 
poor in inclu- 
sions, magne- 
tite. 
V ery rare, 
accessory as 
secondary 
product of de- 
composition of 
olivine in 
gabbro and 
olivine stone. 
Distinguisha- 
ble from bio- 
tite by cleav- 
age amt, of 
pleochroism 
and size of 
axial angle. 
bisectrix (-|-) in 0. j 
Rather 
bril- 
liant. 
cf. 
Bronz- 
ite. 
Light 01 
dark brown, 
black by 
inclusions. 
/ 3 = 1.639 
Pleochroism 
strong. Axial 
colors a= 
hyacinth red 
b=reddish 
brown. 
C=grayish 
green. 
c^>a>b , 
In large 
irregular 
grains in 
granular 
older 
rocks, in 
small crys- 
tals in 
later 
porphyrit- 
ic erup- 
tives. 
With 
plagio- 
clase, 
olivine, 
and 
mono- 
clinic 
augite. 
In the granu- 
lar varieties • 
innumerable 
broun or vio- 
let rectangu- 
lar scales in 
the cleavage 
lines parallel 
i-i. In crys- 
tals regularly 
arranged 
opaque 
needles other- 
wise poor. 
Decom- 
poses into 
fibrous 
aggre- 
gate par- 
allel to 
axis 
with 
dirty 
brown or 
green 
color, as 
enstatite. 
In grains in 
gabbro. nor- 
ites, in later 
eruptives,*par- 
ticularly au- 
gite andesite 
and in feld- 
spathic basalts 
poor in olivine 
as primary 
necessarycom- 
ponent and 
with mono- 
clinic augite. 
Distinguished 
from mono- 
clinic augite 
only by effects 
of convergent: 
polarized 
light, from 
bronzite by 
strong pleo- j 
chroism. ! 
1 
The three rhoixibic augites — enstatite, bronzite and hypersthene are chiefly distinguished 
by variation in amt. of iron, accompanying which a variation in angle of the optical axes lying^ 
in the plane i-i. Rhombic augites distinguished from monoclinic by inferior brilliancy of 
polarization and feebler double refraction. Isotropous sections perpendic. to opt. axis in mono- 
clinic augite exhibit two or three rings and bands while the rhombic at most one and also 
lacks polysynthetic twinning | i-I. 
