metamorphic
Epidosite
Epidosite (Metasomatic rock consisting mainly of Epidote and Quartz)
Hardness: 6-7 (Mohs scale); Color: Distinctive pistachio-green, yellowish-green to murky grey-green; Luster: Vitreous to pearly; Crystal structure: Monoclinic (epidote grains); Cleavage: Perfect in one direction, though usually massive; Specific gravity: 3.2-3.5.
- Hardness
- 6-7 (Mohs scale)
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Distinctive pistachio-green, yellowish-green to murky grey-green; Luster: Vitreous to pearly; Crystal structure: Monoclinic (epidote grains); Cleavage: Perfect in one direction, though usually massive; Specific gravity: 3.2-3.5.
Formation & geological history
Formed through hydrothermal alteration (metasomatism) of mafic volcanic rocks (like basalt or gabbro) where plagioclase feldspar is replaced by epidote. Often found in ophiolite complexes and associated with Precambrian to Mesozoic formations.
Uses & applications
Used primarily as decorative stone, in lapidary work for cabochons or beads (often sold as 'Unakite' when mixed with pink orthoclase), and occasionally as a minor construction aggregate in regions where it is abundant.
Geological facts
Epidosite is a key indicator for geologists looking for massive sulfide deposits, as the hydrothermal fluids that create the green epidote often carry precious metals like copper and gold. It represents a high degree of fluid-rock interaction in the ocean crust.
Field identification & locations
Identify by its 'pistachio green' color and extreme hardness (it will scratch glass). Look for it in riverbeds or coastal areas near former volcanic mountain ranges. Collectors should look for specimens with clear mineral banding or those displaying 'amygdaloidal' (gas bubble) textures filled with the green mineral.
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