}' In sections | to 0 the axial interferance 
aa. Disappearance of the acute 
Ffame. 
Chem. 
Comp, and 
reactions. 
Specif. 
Grav. 
Cleavage. 
Usual com- 
binations Cf 
form of Secs. 
Tzuins 
Opticial 
determtnants 
Double 
Refract 
Colors 
of Po- 
larizn. 
1. Andalusite. 
Chiastolite is a 
variety with sp. 
grav. 2.9-3. 1, 
characterized by 
regularly ar- 
ranged particles 
of carbon in the 
centre and four 
angles Occurs 
in metamorphic 
slates. 
( AI2) Si O5 
Insoluble. 
3.10- 
3-17 
Prismatic 
in I. 
Incom- 
plete in 
i-i, i-i 
and I-i . 
1=90° 
50 ^ 
Fracture 
II 0. 
Long col 
umns I . 0 . 
I-i, more 
rarely gran- 
ular. Trans- 
verse sec- 
tions quad- 
ratic, longit. 
sections 
rectangular 
i 
Opt. axis 
plane |j i-i . 
Acute 
bisectrix 
^0 . 
c=a 
b=b 
a-=c 
Axial angle 
consider- 
able. 
Nega- 
tive, 
strong. 
Bril- 
liant. 
2. Cordierite. 
(Dichroite) 
Finite is a de- 
composition 
product of the 
above, consisting 
of minute fibres 
and scales. 
Mg.2 (R.,) 
Sis 0]8 
(R.) = Al, 
Fe, 
Almost 
insoluble. 
! 
! 
2 - 59 - 
2.66 
i-i 
In comp. 
I-i . 1 = 
119° lO''. 
In large 
grains and 
crystals. 
I . i-i . 0 . 
Hexagonal 
cross sec- 
tions, rect- 
agonal 
longit. 
sections. 
Inter- 
pene- 
trating 
twins 
mult;i- 
ples in 
I, more 
rarely 
in i-3 
Opt. axis 
plane || i-i . 
Acute bi- 
sectrix-L-O. 
c''=a 
b=c 
p<y 
Nega- 
tive, 
feeble. 
Bril- 
liant as 
in 
quartz. 
bb. 
Disappearance of obtuse 
1 7 .oisite. 
H2 Ca^ 
(AI2) 3 Si,j 
^26 
Soluble 
with diffi- 
culty with 
separation 
of gelatin- 
ous silica. 
3.22- 
3-36 
i-i 
Very 
complete 
Fracture 
parallel 
0. 
Elongated 
grains and 
long, trans- 
versely 
jointed 
columns. 
I . i-i , 
I--ii6° 26^ 
Opt. axis 
plane || i-i 
always 
a^=C=+ 
b=b {pfy) 
c'’=a or 
when Opt. 
oxis plane 
II 0 
b— a ipf>v) 
c/=b . 
Feeble 
Bluish 
gi'ay, 
not 
bril- 
liant 
usual- 
ly- 
''^Finite. Large crystals = I . i-i . i-i . O . Polarizes as an aggregate. Occurs with 
quartz, orthoclase and biotite, Easily recognized macroscopically by the character of 
decomposition. 
