II. Double-refractive minerals. 
A. Uniaxial optically. 
I. Tetragonal system, a. Double refraction positive. 
TABLE IV. 
Color and 
amount of 
refraction. 
Pleochro- 
ism. 
Structure. 
Association 
/nclusions. 
Alterations 
Occurrence. 
Remarks. 
Colorless, 
0=1.508 
f:=i.50cj 
Aggregate of 
spherical crys- 
tals to form a 
large crystal. 
Zonal and ra- 
diating ar- 
rangement of 
the inclusions. 
Large corro- 
ded crystals of 
the first order, 
and minute 
sharply de- 
fined crystals 
of second or- 
der, the latter 
often pene- 
trating augite 
With aug- 
ite.olivine. 
plagio- 
clase. and 
sanidine. 
Inclusions 
zonary or ra 
diating, or 
collected in 
a central ag- 
gregate. con- 
sisting of 
minute 
glassy parti- 
cles, gas 
pores, augite 
needles, etc 
as well as of 
Hauyn, au- 
gite, apatite 
and mela- 
ite. 
Into an 
aggregate 
of color- 
less or yel- 
lowish, 
finely radi- 
ating fi- 
bres or 
grains of 
zeolites, 
rarely 
pseudo - 
morphs of 
analcite af- 
ter leucite. 
Primary, es- 
sential const! 
tu'nt with san- 
idine etc. in 
leucitophyres, 
leucite-teph- 
rites, and ba- 
salts, also with 
nepheline and 
plagiolase. 
Only found in 
later basic 
eruptives. 
The foregoing 
characters 
make it easily 
recognizable 
unless It oc- 
curs in very j 
minute grains 
in the magma, 
when it may 
be difficult to 
distinguish it 
from inter- | 
spersed color- 
less areas of 
the glassy ba- 
sis. In this 
case to be rec’j 
ognized microj 
chemically. | 
Hon’y yel- 
low to red- 
dish 
brown, 
grains oft- 
en opacjue 
or merely 
transluc’nt 
( Nigrine ) , 
in which 
case with 
(incom- 
plete) me- 
tallic lus- 
tre. 
Not par- 
ticularly 
noticeable 
i 
: 1 
In biotite fre- 
quently very 
regular com- 
pounded into 
“sagenite” 
forms, also 
united to ti- 
tanic iron. 
Often as an 
inclusion in 
the accom- 
panying min- 
erals, particu- 
larly garnet 
and ompha- 
cite. 
With 
quartz, pot 
ash feld- 
spar, gar- 
net, horn- 
blende, 
omphacite 
Very poor. 
i 
As primary ac- 
cessory com- 
ponent abun- 
dant in near- 
ly all crystal- 
line slates, par-, 
ticularly those 
bearing horn- 
blende and 
augite, as am- 
phibolites and 
eklogit’s. Also 
as secondary 
dec'mposition 
product of ti- 
tanic iron, 
frequent in 
clay slates. 
Easily distin-j 
guished from; 
zircon by the| 
polarization ! 
colors, color j 
and tendency! 
to twin. j 
i 
j 
Colorless, 
wine yel- 
low. Re- 
fraction 
strong, 
hence 
dark con- 
toured (by 
total reflec 
tion). 
1 .92 
£=1.97 
j Not no- 
i ticeable. 
1 
Like rutile, 
one of the first 
formed com- 
ponents of 
rocks and 
therefore fre- 
quent as in- 
clusions in the 
others. 
With 
quartz, or- 
thoclase, 
biotile, 
horn- 
blende, 
augite. 
Fluid inclu- 
sions, nee- 
dle-shaped 
cavities, and 
long uniden- 
tified nee- 
dles. 
- 
Primary ac- 
cesory compo- 
nent of gran- 
ite, syenite, 
quartz -por- 
phyry, trach- 
ytes and many 
other eruptive 
rocks.but rare. 
More frequ’nt 
in crystalline 
slates with 
rutile. 
Well charac- 
terized by the 
crystalline 
form, polar- 
ization colors,! 
and strong j 
double refrac-j 
tion. ; 
1 
i 
1 
I 
