Mineral - Staurolite
Staurolite
Chemical Properties
Mineral Class
Silicates
Toxicity
none
Formula
(Fe²⁺)₂Al₉Si₄O₂₃(OH)
Unit Cell
a=7.87 b=16.61 c=5.66 β=90° Z=2
Physical Properties
Hardness
7 - 7.5
Streak
white
Density
Normal (2-3,5)
Cleavage
Distinct after {010}
Fracture
conchoidal
Tenacity
Brittle
Optical Properties
Color
blackbrown
Birefringence
0.015
Luster
Vitreous,
Greasy
Transparency
opaque
Pleochroism
Geomineralogical Properties
Crystal System
monoclinic
Point Group
monoclinic-prismatic - 2/m
Space Group
C2/m (12)
Habit
lath-shaped, prismatic, tabular
Formation
Regional metamorphic rock formed by the metamorphism of aluminum-rich, pelitic sediments (metapelites) under amphibolite facies conditions (approx. 500–700 °C, moderate pressure).
Paragenesis
Twinning
Cross-shaped 90° penetration twins after {031}, X-shaped 60° penetration twins after {231}. Both types of twins may also occur together
Rarity
Common
Synonyms
Staurolite
Composition
Elements
Mass
SiO₂
27.82
TiO₂
0.32
Al₂O₃
54.91
Fe₂O₃
0.43
Cr₂O₃
0.01
FeO
12.39
MnO
0.22
CoO
0.02
ZnO
0.19
MgO
0.62
Li₂O
0.36
H₂O
2.26
New Hampshire (Dana 1895)
Groups and Members
Staurolite-Group