igneous
Epidote in Basalt
Epidotized Basalt (Ca2(Al2,Fe)(SiO4)(Si2O7)O(OH) in Mafic Igneous Host)
Hardness: 6-7 (Mohs scale); Color: Pistachio green to yellowish-green (epidote) against dark grey/black (basalt); Luster: Vitreous to dull; Crystal structure: Monoclinic; Cleavage: Perfect in one direction for epidote crystals.
- Hardness
- 6-7 (Mohs scale)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Pistachio green to yellowish-green (epidote) against dark grey/black (basalt); Luster: Vitreous to dull; Crystal structure: Monoclinic; Cleavage: Perfect in one direction for epidote crystals.
Formation & geological history
Formed via hydrothermal alteration or low-grade metamorphism (greenschist facies) where hot, mineral-rich fluids react with calcium-rich plagioclase feldspar and pyroxene within basaltic rock.
Uses & applications
Primarily used as a decorative stone, semi-precious gemstone (Unakite variety if with pink feldspar), or as industrial crushed stone and road aggregate.
Geological facts
Epidote gets its name from the Greek word 'epidosis' meaning 'addition', referring to the crystal's base having one side longer than the other. The green color is a direct result of iron content within the mineral structure.
Field identification & locations
Identify in the field by looking for the distinctive 'pistachio green' color in veins or patches within dark, fine-grained volcanic rocks. Commonly found in areas with past volcanic activity like Lake Superior (USA), Norway, and the Alps.
