II. b. 2. Monoclinic minerals. 
a. Apparently hexagonal (or rhombic) ; highly perfect cleavage parallel O. 
Name. 
I Chemical 
comp, and 
reactions. 
Specific 
gravity 
Cleavage. 
Usual combi- 
nations and 
form of sec's. 
Twins. 
Optical deter 
minants. 
Dotdde re 
fraction. 
i.Mica Group 
Mixture of 
28-3.2 
11 0 very 
I almost 120° 
Rare. 
Opt. axial 
N egative. 
a. Meroxene. 
(Ala)^ 
perfect. 
I. i-P. 0. 
Twin- 
plane j i-i^ 
'Apparent- 
{Biotite) 
iSi, H3 0,, 
Separati’g 
Thin plates or 
j niiig 
and parallel 
ly perpen- 
b. Rubelane. 
and Mg^3 
in -1-3^ 
short columns. 
j plane 
two opposite 
dicular ex- 
Differs in the 
Si,. 0 .^^ in 
and 
Sections par 
I. Indi 
sides of the 
tinction & 
brownish red 
ratio of 
(i-i) cor- 
allel to 0 are 
vidu’ls 
hexagon 
small axial 
or seal red col 
i:i or 1:2 
respondi’g 
hexagonal 
distort'd 
Acute bisec- 
angle 
or from biotite 
(Tscher- 
to sliding 
plates without 
so as to 
trix vary- 
make it 
of which it 
mak) De- 
or pres 
fracture lines. 
be at- 
ing little from 
appear 
seems to be a 
composed 
sure 
Often with 
tached 
the per pen 
hexagonal 
pyrogene pro- 
by H., SO, 
planes. 
sliding planes 
in a ! 
dicular to 0. 
Cross sec- 
duct of altera- 
c’mpletely 
and three sys- 
plane al-| 
Axial angle 
tions ap- 
tion. Occurs 
with for- 
tems of lines 
most par 
usually very 
parently 
in basalts and 
Illation of 
intersecting at 
allel to 
small =c^°- 
isotropous 
lava. 
skeleton of 
60°. The Ion 
0 . Often 
1.3°, variable,- 
In con- 
c. Phlogopite. 
silica. 
gitudinal sec 
inPrlam- 
occasionally 
vergent 
Can be distin- 
tion rectangu 
ellated 
large, varying 
polarized 
guished by 
lar with nu- 
when 
with the 
light appa- 
chemical an- 
merous cleav 
only rec- 
amount of 
rently hex- 
alysis and the 
age lines par- 
ogniza 
iron. Disp. 
agonal. 
yellow or light 
allel to axis U . 
ble in po 
p<u. 
brown color 
larized 
A magnesia 
light. ] 
mica nearly 
According 
Optical axis 
free'from iron 
to Tscher- 
As in 
As in merox- 
1 
planes -I- i-i' 
Negative. 
mak, a 
meroxene. 
ene. 
a almost -L 0. 
Extinction 
d. Anomite\N\y.\.wx& of 
i 
Axial angle 
perpendic- 
(Biotite-pars) 
H, K, 
12-16° Disp. 
ular. 
1 (Al.,h, Si, 
v<p. 
e. Muscovite 
0-24 and 
2.76- 
Very per 
Rarely crys- 
! 
(and Sericite) 
I Mgi2 Si, 
3-1 
feet paral- 
tallized in 
As me- 
Optical axis 
Negative, 
O24 in ra- 
lel to 0 . 
rocks. Six 
roxene. 
plane i-i^ a 
strong. 
tio i: I or 
Sliding 
sided plates. 
i 
slightly varies 
Extinction 
2:1. 
i 
planes. 
from U, a al- 
perpen- 
most -^,.to 0 
dicular. 
; H4 K2 
1 
Disp pP>v. 
Apparent- 
(AI2 ), Si, 
1 
axial angle 
ly rhomb- 
O24. Insol- 
usually large. 
ic. 
uble. 
1 
60-70°. 
H2 Mg 3 
2. Talc. 
Si 4 O12. 
2.69- 
Perfect 
Never in crys- 
Optical axis 
Negative, 
i 
Unattack- 
2.8 
11 Oj (in- 
tals, in rocks 
j 
plane || i-i^, || 
feeble. 
ed by 
complete 
usually as mi- 
■ 
to a line of 
Extinction 
acids. Al- 
I-) 
nute irregular 
fracture, a 
apparent- 
3. Chlorite 
kaline re 
plates like 
almost at -J- 
ly rhomb- 
Grotip. 
action. 
mica. 
i 
to 0. 
ic. 
a. Ripidolite 
Mixture 
1 
(b. Clinoch 
of p(2 H2 
2,7- 
Perfect 
Scales and 
t 
Although oft- 
Negative, 
lor mon’clinic 
0. 3MgO 
2 * 95 - 
II 0. 
hexagonal 
en seeming 
feeble. 
habit, strong 
2 Si O2 ) + 
plates I. 0. as 
hexagonal yet 
pleochroism. 
y(2H2 0. 
though hex- 
sometimes 
Semicryst. 
2Mg 0 
agonal. If 
1 ( 
obviously bi- 
and metamor- 
AI2 O3 Si 
monoclinic I. 
, 
axial with 
phic.) ; 
O2 ). 
i-P.O. 
small axial 
1 
angle a-^O. 
