Mineral - Epidote
Epidote
Chemical Properties
Mineral Class
Silicates
Toxicity
none
Formula
Ca₂(Fe³⁺,Al)Al₂[O|OH|SiO₄|Si₂O₇]
Unit Cell
a=8.89 b=5.63 c=10.15 β=115° Z=2
Physical Properties
Hardness
6 - 7
Streak
white
Density
Normal (2-3,5)
Cleavage
Perfect after {001}, imperfect after {100}
Fracture
uneven
Tenacity
Brittle
Optical Properties
Color
browngreen
Birefringence
0.046
Luster
Vitreous
Transparency
translucent,
transparent,
opaque
Pleochroism
X: Grün-Farblos
Y: Grün-Gelb
Z: Gelb-Grün
Geomineralogical Properties
Crystal System
monoclinic
Point Group
monoclinic-prismatic - 2/m
Space Group
P2 1 /m (11)
Habit
fibrous, massive, prismatic, prismatic
Formation
(1) Metamorphic, formed by the transformation of calcium-aluminum silicates under conditions ranging from the green schist to the amphibolite facies.
(2) Hydrothermal, resulting from the alteration of calcium-rich plagioclases in igneous rocks.
(3) Metasomatic, as a major component of calc-silicate rock (skarn) in the contact zone between acidic intrusions and carbonate rocks.
Paragenesis
Twinning
Rarity
Common
Synonyms
Epidote
Composition
Elements
Mass
SiO₂
36.52
Al₂O₃
20.97
Fe₂O₃
17.22
FeO
0.45
CaO
23.05
H₂O
1.98
USA (Dana 1895)
Groups and Members
Epidote-Supergroup
Epidote-Group