(e.) Arfvedsonitc. Na2 (Fcg'' Si^ O12. Specif, gr. 3.33-3. 59 - Occurs in large 
grains cleaving in I, with orthoclase, microcline. elaeolite and sodalite, rarely in elaeolite 
rocks. It is distinguished from hornblende by blue-green color and composition . 
(b.) Glaucophane. Nag ( Alg ) Si4 O12 with Ca Mg. and Fe. Specif, gr. 3.1. 
It is an indigo blue mineral with strong pleochroism occurring, in long fibrous needles 
dd. Cleavage 1 | O and i-i ; angle 115°. 
Name. 
Chemical 
comp, and 
reactio 7 is. 
Specific 
gravity 
Cleavage. 
Usual co 7 nbi- 
nations and 
form of sec's. 
Twins. 
Optical deter- 
minants. 
Double re- 
fi'action. 
Epidote. 
H2 Ca 4 
( R 2 )3 Sie 
026 - 
3-32- 
3-5 
1 
1 0 perfect 
and i_i 
forming 
angle of 
115° 24^ 
Extended in 
the ortho-di- 
agonal, gen- 
erally small 
columns I. 0 . 
i-i. i_i. Lon- 
gitudinal sec- 
tions 1 i_F 
hexagonal. 
Cross sections 
II O: i_i elong 
ate quadrang- 
ular or ex- 
tended hex- 
agonal. Also 
in grains. 
Plane i_i 
Rarely 
micro- 
scopic. 
Optical axis 
plane 1 i-i^ 
b=b acute 
bisectrix =a 
nearly coin - 
cides with c. 
Sections || to 
i-i show a bi- 
axial interfer- 
ence figure. ' 
Negative, 
strong. 
Extinction 
a: c=2° 
20^, 
c: U--=2fi 
47^=c:0. 
ee. Cleavage imperfect in I or 
Titafiite. 
Ca Si Ti 
O5. De- 
composed 
by H-2 SO^ 
1 Ti O2 is 
jdissolved, 
and gyp- 
! sum 
formed. 
3 -T 3-6 
I 133° 55 " 
i-F 113° 
30^ im- 
perfect. 
Usually crys- 
talline I. 0 . 
/^(i-F.) Yz 
(1-2") or 
(1-2^). Or in 
wedge-shaped 
grains. 
Rather 
frequent 
Contact 
or inter 
pene- 
trating 
twins in 
plane O. 
Optical axis 
plane || i-i^ 
acute bisectrix 
=<:almost per- 
pendicular to 
I-i) strong 
dispersion of 
axes. 
Positive; 
strong. 
Extinction 
a: c=39° 
I7^a-a^= 
21°. 
1 
1 
Gypsum. 
Ca SO4+ 
2 Aq. Sol- 
uble in 
acids with 
difficulty. 
2, 2-2.4 
Complete 
in the cli- 
nodiago- 
Inal, less so 
-I. 
In grains or 
long colamnar 
individuals. 
Crystals I. 
i-F. -I. 
Rare in 
micro- 
scopic 
individ- 
uals. 
Optical axis 
plane || i-F 
Acute bisect. 
=«. One op- 
tical axis al- 
most -L i-i 
forming with 
c an angle of 
83°, the other 
an angle of 
22°. 
Negative 
strong. 
Extinc- 
tion 
a: c=52° 
30^ 
C: c= 37 ° 
30C 
