! 
Na?iie. 
Chemical Comp, 
and reactions. 
Specif. 
Grav. 
Cleaz' 
age. 
Usual combi- 
natiotis and 
form of Seds. 
Twins. 
Color and 
and amt. 
of refract 
Structure. 
c. Mel 
anite 
Ca3 (Fe.jSigOj, 
• 
1 
^ J 
3 - 0 - 4-3 
Incom-. 
plete. 
i 
Crystals 
Black, in 
sections 
dark 
brown, 
quite 
opaque. 
Often with 
beautiful 
zonary struc- 
ture, then 
often double 
refracting. 
3. Spinel 
Group. 
' a. Chro 
mite. 
b. Pico- 
tite. 
c. Pleo- 
nast. 
d. Her- 
cynite. 
Fe 0 Cr2 O3 
MgOrAl.,031 
Fe 0101403/ 
FeO [A 1 .^ O3/ 
MgO\Fe, O3I 
Fe 0 . AI2 0.. 
Insoluble in 
acids and unaf-! 
fected by H FI. j 
4.4-4. 6 
4 S 
Over 
3.6s 
(3.8-4. 1) 
Incom- 
plete. 
I . 
Granular 
and I. 
I. 
Very minute 
grains. 
I. 
Twins 
in I. 
Reddish 
brown, 
metalic 
lustre 
Becomes 
transpar- 
ent with 
difficulty 
Isolated 
grains often 
found in 
basalts with 
a broad sub- 
opaque 
bqrcler. 
Dark 
green 
Frequ'nt 
with 
quartz, 
ortho 
clase, 
and mica 
Often 
double re 
fractive and 
with a dis- 
tinct zonary 
structure 
gf nerally 
cloudy, com- 
bined with 
plagioclase 
4. Anal- 
cite. 
Na2(Al2) 1 
Soluble in H 
Cl vdth sep of 
Si 0-2 jelly. 
i 
2. 1-2.28 
Incom- 
plete. 
(Ac- 
cord- 
ing 
to 
Tsch- 
ermak 
H.) 
Chiefly 
compact 
granular, 
in cavities 
Colorless 
white, 
np= 
1.4874 
[ 
Penetrating 
feldspar.and 
irregularly 
distributed 
in the 
magma. 
5. Fluor- 
ite. 
Ca FI 2 . 
Decomposed by 
concentrated 
H2 SO^ with 
liberation of 
H FL 
3.1-32 
( lom- 
plete 
I. 
1 
Occurs in 
rocks only in 
the form of 
Iminute an- 
gular grains. 
Blue, 
colorless. 
! very 
strongly 
refrac- 
tive. 
Characteris- 
tic is the 
rough sur- 
face of a sec- 
tion . Group- 
ed as inclu- 
•sions in mel- 
iliie or oli- 
vine. Often 
exhibiting 
double re- 
fraction. 
Colors of 
polarization 
not bright. 
6. Pe- 
rowskite. 
Ca Ti 0.3 . 
Decomposed in 
H2 SO^ but not 
M Cl. 
4.0-4. 1 
H. 
! In irregu- 
lar branch- 
ing and an- 
gular forms, 
generally in 
distinct oc- 
tahedrons. 
Very 
rare. 
In ter- 
pen e- 
tra ting 
twins. 
Violet 
gray,’’ 
reddish 
gi-ay 
brown. 
In strong 
relief. 
i 
i 
i 
Mineral appearing regular 
