metamorphic
Epidote in Granite Gneiss
Epidote bearing Orthogneiss (Ca2(Al,Fe)3(SiO4)3(OH))
Hardness: 6-7 (Mohs scale); Color: Pistachio green (Epidote) mixed with pink/white feldspar and gray quartz; Luster: Vitreous to dull; Structure: Gneissic foliation with pistachio-green mineral bands; Specific gravity: Approx 2.6 - 3.4.
- Hardness
- 6-7 (Mohs scale)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Pistachio green (Epidote) mixed with pink/white feldspar and gray quartz; Luster: Vitreous to dull; Structure: Gneissic foliation with pistachio-green mineral bands; Specific gravity: Approx 2.6 - 3.4.
Formation & geological history
Formed via regional metamorphism of igneous granite. The green epidote band suggests hydrothermal alteration or low-to-medium grade metamorphism (greenschist facies) where plagioclase feldspar is replaced by epidote minerals. Age is typically Proterozoic to Paleozoic depending on region.
Uses & applications
Primarily used as decorative stone, construction aggregate, or as a geological teaching specimen. Polished pieces are used in lapidary work and 'unakitization' related stones are used for beads.
Geological facts
The distinctive 'pistachio green' color of the epidote is a primary indicator of its presence. When found with pink orthoclase, it is often referred to by lapidaries as Unakite, though this specimen shows more distinct gneissic banding.
Field identification & locations
Identify in the field by the high-contrast green 'mossy' streaks against a granitic background and its high hardness (cannot be scratched by a steel nail). Commonly found in high-grade metamorphic terrains and riverbeds near ancient mountain belts.
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