metamorphic
Epidosite (Epidote-rich rock)
Epidosite (consisting primarily of Epidote: {Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH))
Hardness: 6-7 on Mohs scale; Color: Distinctive pistachio-green to yellowish-green; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect in one direction; Specific gravity: 3.3-3.6
- Hardness
- 6-7 on Mohs scale
- Color
- Distinctive pistachio-green to yellowish-green
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Distinctive pistachio-green to yellowish-green; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect in one direction; Specific gravity: 3.3-3.6
Formation & geological history
Formed via hydrothermal alteration or low-to-medium grade regional metamorphism of mafic igneous rocks (like basalt). It often occurs in 'greenstone' belts where calcium-rich minerals are replaced by epidote through the interaction of hot, mineral-rich fluids.
Uses & applications
Primarily used as a decorative stone, and occasionally in jewelry as a minor gemstone (known as Unakite when mixed with pink feldspar). It also serves as an indicator mineral for geologists searching for hydrothermal ore deposits.
Geological facts
The name comes from the Greek word 'epidosis', meaning 'addition', referring to the crystal's characteristic of having one side longer than the other at the base of the prism. Fine specimens are often found in the Alps and the Ural Mountains.
Field identification & locations
Identify in the field by its unique 'pistachio' green color and its association with quartz or basalt. Common in mountainous regions with a history of volcanic activity. For collectors, it is often found in riverbeds as rounded, waxy pebbles.
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