Chemistry Reference
In-Depth Information
Birefringence
Indices
balsam1,54
quartz
crystalline forms − cleavages − twine
position of the indicatrix
Name
Chemical formula
Color
Alterations
Uniaxial
/Biaxial
+ / −
2d −
3rd
order:
bright
colors
higher
orders:
whashed
colors
1st order
tourmaline
garnet
0
0,009
0,018
0,054
Micas
Muscovite
KAI
3
Si
3
O
12
(OH)
2
Biotite
K(Fe,Mg, Ti)
3
Si
3
O
12
(OH)
2
Si (Fe,Mg) = AI
IV
AI
IV
Chlorites
(Fe,Mg)
6−x
AI
2x
Si
4−x
O
10
(OH)
8
mnocl
Colorless
(pale green:
phengites)
red brown
dark brown
greenish
colorless
(Mg)
α
pseudo
hex
positive
elongation
B−
(2V = 35−50°)
γ
(biotite)
β
B−
(2V = 0−35°)
(muscovite)
longitudinal section
basal section
α/γ
mnocl
anomalous
in
terference colors:
gr
ay, green gray
olive gr
een, purplish blue
same forms
as micas
green
colorless
B+/−
positive or negative elongation
colorless
(Mg)
green(Fe)
red brown
yellow brown
(Fe
3+
, Ti)
blue
blue green
dark green
colorless
(Mg)
greenish
(Fe)
purplish
brown
(Ti)
colorless
(pale brown
pale green
pinkish)
colorless
Amphiboles
A
0−1
X
2
Y
5
Z
8
O
22
(OH)
2
mnocl
γ
<30°
X= Ca calcic amphiboles
non AI : tremolite − actinote
55−56
°
B−
AI : hornblendes
simple twin
X = Na sodic amphiboles
longitudinal
section
glaucophane
basal section
(100)
riebeckite
arfvedsonite
Pyroxènes
Clinopyroxenes
(Ca,Mg,Fe
2+
(Na, AI,Fe
3+
))
2
Si
2
O
6
106°
38−43°
γ
mnocl
B+
(100)
93°
(001)
aegyrine
Orthopyroxenes
(Mg,Fe
2+
)
2
Si
2
O
6
orthor
B+/−
(100)
(100)
basal section
orthor
α
Olivines
(Mg,Fe
2+
)
2
SiO
6
γ
B+/−
serpentine
iddingsite
(010)
Figure 3.27
Summary of the characters of the major ferro-magnesian minerals.
