metamorphic
Epidote in Matrix
Epidote; Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
Hardness: 6-7 on Mohs scale. Color: Distinctive pistachio-green to yellowish-green streaks on a dark/reddish groundmass. Luster: Vitreous to pearly. Crystal structure: Monoclinic, often appearing as fibrous or granular coatings in matrix.
- Hardness
- 6-7 on Mohs scale
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Distinctive pistachio-green to yellowish-green streaks on a dark/reddish groundmass. Luster: Vitreous to pearly. Crystal structure: Monoclinic, often appearing as fibrous or granular coatings in matrix.
Formation & geological history
Formed through low-to-medium grade regional metamorphism or hydrothermal alteration of igneous rocks. It commonly occurs in association with chlorite and quartz in basaltic or gabbroic host rocks.
Uses & applications
Commonly used as a decorative stone or lapidary material. High-quality crystal specimens are sought by mineral collectors. Industrially, it is an indicator mineral for metamorphic facies.
Geological facts
Epidote is a classic 'index mineral' for the greenschist facies. Its name comes from the Greek word 'epidosis', meaning 'addition', in reference to one side of the prism being longer than the other.
Field identification & locations
Identify in the field by its unique 'pistachio' green color. Common in areas with volcanic activity or where mountain building has occurred, such as the Appalachian or Cascade ranges.
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