monoclinic Sorosilicates
Epidote
Formula Ca2(Al,Fe)3(SiO4)3(OH)
Crystal Structure
#! Species: Epidote
#! System: Monoclinic (2/m)
#! Habit: Elongated prismatic with characteristic striations
monoclinic[2/m]:{100}@1.0[striation:parallel] + {001}@0.8 + {010}@0.7 + {110}@0.5
monoclinic
2/m
{100} {001} {010} {110}
Quick Facts
Hardness
6.0
Specific Gravity
3.35
Refractive Index
1.729
Optical Character
Biaxial -
Physical Properties
- Crystal System
- monoclinic
- Hardness (Mohs)
- 6.0
- Specific Gravity
- 3.35
- Cleavage
- Perfect {001}, imperfect {100}
- Fracture
- Uneven
- Lustre
- Vitreous
Optical Properties
- Refractive Index
- 1.729
- Birefringence
- 0.019-0.046
- Optical Character
- Biaxial -
- Dispersion
- 0.03
- Pleochroism
- strong: Pistachio green / Brown / Yellow (Distinctive trichroism; colors may appear as root beer and olive-green)
Characteristics
Colours
Pistachio greenYellowish-greenDark greenBrownish-greenBlack (iron-rich)
Localities
Austria (Knappenwand - type locality, world-class specimens)Pakistan (gem crystals)PeruUSA (Alaska, California)BrazilNorway
Crystal Forms
prismpinacoid
Notes
Variable birefringence depending on iron content; high relief in thin section
Related Minerals
Other minerals in the monoclinic system
