Mineral - Sturmanite
Sturmanite
Chemical Properties
Mineral Class
Sulphates
Toxicity
none
Formula
Ca₆Fe³⁺₂(SO₄)₂,5[B(OH)₄](OH)₁₂ · 25H₂O
Unit Cell
a=11.16 c=21.79 Z=2
Physical Properties
Hardness
2.5
Streak
yellow
Density
Light (<2)
Cleavage
Perfect after {10 1 0}
Fracture
uneven
Tenacity
Brittle
Optical Properties
Color
brownorangeyellow
Birefringence
0.005
Luster
Vitreous,
Greasy
Transparency
translucent,
transparent,
opaque
Pleochroism
Geomineralogical Properties
Crystal System
trigonal
Point Group
ditrigonal-pyramidal - 3m
Space Group
P31c (159)
Habit
blocky, dipyramidal, lenticular, prismatic, tabular, barrel-shaped
Formation
Secondary, formed under low-temperature hydrothermal conditions in fractures and cavities of metasomatically altered manganese deposits
Paragenesis
Twinning
Rarity
Very rare
Synonyms
Sturmanite
Composition
Elements
Mass
SO₃
14.20
B₂O₃
3.20
Al₂O₃
1.13
Fe₂O₃
8.84
MnO
1.30
CaO
25.60
H₂O
46.70
South Africa (Peacor et al. 1983)
Groups and Members
Ettringite-Group