metamorphic
Epidotite (Unakite variety)
Epidotized Granite (Ca2(Al2,Fe)(SiO4)(Si2O7)O(OH))
Hardness: 6-7 Mohs; Color: Pervasive pistachio-green with potential pink feldspar inclusions; Luster: Vitreous to dull; Crystal structure: Monoclinic; Cleavage: One direction (perfect), though usually massive; Specific gravity: 3.2-3.5.
- Hardness
- 6-7 Mohs
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 Mohs; Color: Pervasive pistachio-green with potential pink feldspar inclusions; Luster: Vitreous to dull; Crystal structure: Monoclinic; Cleavage: One direction (perfect), though usually massive; Specific gravity: 3.2-3.5.
Formation & geological history
Formed through hydrothermal metamorphism (metasomatism) where plagioclase feldspar is replaced by epidote. Usually associated with crystalline basement rocks of Proterozoic age.
Uses & applications
Used primarily as a decorative stone, semi-precious gemstone for cabochons, lapidary work, and architectural stone. Also used in crushed form for construction aggregate.
Geological facts
Epidote gets its name from the Greek word 'epidosis' meaning 'addition' or 'increase,' referring to the base of the crystal being longer on one side. This specific green variety is often found mixed with pink orthoclase in the rock Unakite.
Field identification & locations
Identify in the field by its distinct 'pistachio' or 'apple' green color and high hardness (it will scratch glass). Commonly found in the Blue Ridge Mountains of the USA, as well as Norway and South Africa. Collectors should look for vibrant color saturation.
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