Chemistry Reference
In-Depth Information
Birefringence
Indices
balsam1 54
quartz
2d−3rd
orders
bright
colors
0,0
54
Name
chemical formula
crystalline forms−cleavages−twin
s
position of the ind
icatrix
Color
Alterations
1st order
Uniaxial/
Biaxial
+/−
higher
orders
colors
tourmaline garnet
0,009
0,018
γ
orthor
pseudo
tetr
poikiloblasts − chiastolite variety
Andalusite
Al
2
SiO
5
colorless
(pink)
B−
(2V = 83−85˚)
89˚
β
α
basal
section
longitudinal section
transversal fractures
α
Sillimanite
Al
2
SiO
5
orthor
γ
colorless
(fibrolite:
brownish)
longitudinal se
ction
B+
(2V = 21−30˚)
β
basal
section
fibrolite
(010)
α
γ
76˚
30˚
Kyanite
Al
2
SiO
5
tricl
colorless
(plae blue)
B−
(2V = 82˚)
longitudinal section
103˚
basal section
β
Staurolite
(Fe,Mg,Zn)
2
Al
9
Si
4
O
22
(OH)
2
orthor
yellow
plae yellow
golden
yellow
B+
(2V = 84−88˚)
γ
α
longitudinal section
poikiloblasts
basal section
γ
mnocl
/tricl
5−25˚
radiating
associatons
Chloritoid
anomalous
grey green,
olive green
colors
grey green
olive green
B+
(2V = 36−70˚)
(001) twin
(Fe,Mg,Mn)
2
(Al Fe
3+
)Al
2
Si
2
O
10
(OH)
4
β
/
α
Cordierite
(Mg,Fe)
2
Al
4
Si
5
O
18
orthor
pseudo
hex
colorless
alteration into
yellow
isotropic products
/muscovite
yellow pleochr.
halos on ziroon
60˚polysynthetic
twins
at high
temperature
B−
(2V =
42−104˚)
γ
α
longitudinal section
poikiloblasts
β
Garnet
(Fe,Mg,Mn,Ca)
3
(Al,Fe
3+
)
2
Si
3
O
12
cub
trapezoedron
dodecaedron
isotropic
calcic garnets
often have a weak
blrefringence
colorless
(pink
brown
brown green)
polkloblasts
Figure 3.34
Summary of the characters of the aluminous minerals.
