metamorphic
Epidote
Epidote (Ca2(Al, Fe)3(SiO4)3(OH))
Hardness: 6-7 Mohs; Color: pistacchio green, yellowish-green to black; Luster: vitreous to pearly; Crystal structure: monoclinic; Cleavage: perfect in one direction; Specific gravity: 3.3-3.6.
- Hardness
- 6-7 Mohs
- Color
- pistacchio green, yellowish-green to black
- Luster
- vitreous to pearly
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Physical properties
Hardness: 6-7 Mohs; Color: pistacchio green, yellowish-green to black; Luster: vitreous to pearly; Crystal structure: monoclinic; Cleavage: perfect in one direction; Specific gravity: 3.3-3.6.
Formation & geological history
Forms primarily in regional and contact metamorphic rocks, particularly those of low to medium grade like greenstone. It typically results from the hydrothermal alteration of various minerals such as feldspar and pyroxene.
Uses & applications
Primarily used as a minor semi-precious gemstone or as a collector's specimen. It is also an indicator mineral for the presence of metamorphic zones during geological mapping.
Geological facts
The name 'epidote' comes from the Greek word 'epidosis', meaning 'addition', referring to the unequal sides of the crystal base. It is a defining mineral of the 'greenschist facies' in metamorphic petrology.
Field identification & locations
Identify by its characteristic pistachio-green color and hardness that scratches glass but not quartz. Common in alpine veins and regional metamorphic terrains such as the Alps, Norway, and California.
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