Chemistry Reference
In-Depth Information
Birefringence
crystalline forms−cleavages−twins
position of the indicatrix
Indices
balsam1,54
quartz
Name
Chemical formula
Color
Alterations
Uniaxial/
Biaxial
+/−
2nd−3rd
orders:
bright
colors
higher
orders:
whashed
colors
1st order
tourmaline
garnet
0
0,009
0,018
0,054
Quartz
Sio
2
hex
most times anhedral
high temperature (volcanic rocks)
no cleavage
incolorless
no
altérations
ε
U+
short prism and dipyaramid
(trig
at T>
573
°
C)
low temperature
elongated prisms
chalcedony
ε
positive elongation
embayments
basal section
Feldspars
potassium feldspar
incolore
perthites (in the FK)
angle between
the cleavages
(001)−(010)
90
°
90
°
90
°
39'
B−
(001)
alterations:
KAISi
3
O
8
sanidine
orthoclase
microcline
mnocl
mnocl
staining
tricl
section parallel
to (100)
116
°
plagioclases
NaAISi
3
O
8
tricl
93−94
°
albite
oligoclase
andésine
labrador
bytownite
anorthite
section parallel to (010)
sericitization
saussuri-
tization
B−
twins
simple: Carlsbad,
Baveno, Manebach
polysynthetic (plagioclases):
albite (010)
péricline [010]
(001)
87−86i
CaAI
2
Si
2
O
8
macle de
l'albite
colorless
easily
altered
cancrinite
colorless
Nepheline
NaAISiO
4
hex
short hexagonal prisms
U−
ε
basal section
negative elongation
Leucite
KAISi
2
O
6
tetr
pseudo
cub
trapozoedron = leucitoedron
polysynthétic twins
Sodalite − Haüyne −
Noseane
(Na,Ca)
8
(AISiO
4
)
6
(Cl,SO
4
)
1−2
cub
colorless
(bluish)
cleavage (110)
Figure 3.10
Summary of the characters of quartz, feldspars and feldspathoids.
