metamorphic
Epidote (likely Pistacite in Epidosite rock)
Epidote: Ca2(Al,Fe)3(SiO4)3(OH)
Hardness: 6-7 Mohs; Color: Pistachio-green to dark olive green; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect in one direction; Specific gravity: 3.3 to 3.5.
- Hardness
- 6-7 Mohs
- Color
- Pistachio-green to dark olive green
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 Mohs; Color: Pistachio-green to dark olive green; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect in one direction; Specific gravity: 3.3 to 3.5.
Formation & geological history
Formed through regional or contact metamorphism of rocks such as basalt or gabbro. It often appears in hydrothermal alteration zones and may range in age from Precambrian to more recent tectonic events.
Uses & applications
Used primarily as a collector's mineral and semi-precious gemstone. In massive form (Epidosite), it is sometimes used as a minor decorative stone or in landscaping.
Geological facts
The name 'Epidote' comes from the Greek word 'epidosis', meaning 'addition', referring to the crystal's unequal sides. It is a common indicator of low-grade metamorphism (Greenschist facies).
Field identification & locations
Identify in the field by its distinct 'pistachio green' color and high hardness (it can scratch glass). Commonly found in the Blue Ridge Mountains (USA), the Alps, and Alaska. Collectors should look for it in stream beds where volcanic rocks have weathered.
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