monoclinic Sorosilicates
Epidote
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 -
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Open in PlaygroundPhysical Properties
Crystal Systemmonoclinic
Hardness (Mohs)6.0
Specific Gravity3.35
CleavagePerfect {001}, imperfect {100}
FractureUneven
LustreVitreous
Optical Properties
Refractive Index1.729
Birefringence0.019-0.046
Optical CharacterBiaxial -
Dispersion0.03
Pleochroismstrong: Pistachio green / Brown / Yellow (Distinctive trichroism; colors may appear as root beer and olive-green)
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
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Open in PlaygroundRelated Minerals
Other minerals in the monoclinic system
