Mineral - Ettringite
Ettringite
Chemical Properties
Mineral Class
Sulphates
Toxicity
none
Formula
Ca₆Al₂[(OH)₁₂|(SO₄)₃]·26 H₂O
Unit Cell
a=11.23 c=21.44 Z=2
Physical Properties
Hardness
2 - 2.5
Streak
white
Density
Light (<2)
Cleavage
Perfect after {10 1 0}
Fracture
uneven
Tenacity
Brittle
Optical Properties
Color
whiteyellow
Birefringence
0.021
Luster
Vitreous,
Silky
Transparency
translucent,
transparent
Pleochroism
Geomineralogical Properties
Crystal System
trigonal
Point Group
ditrigonal-pyramidal - 3m
Space Group
P31c (159)
Habit
blocky, prismatic, prismatic
Formation
hydrothermal, Metamorphose
Paragenesis
Twinning
Rarity
Very rare
Synonyms
Ettringite, Woodfordite
Composition
Elements
Mass
SO₃
18.80
CO₂
0.80
Al₂O₃
7.00
CaO
26.60
H₂O
46.30
Ireland (Palache et al. 1951)
Groups and Members
Ettringite-Group