metamorphic
Epidote with Unakite characteristics
{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
Hardness: 6–7 on Mohs scale. Color: Pistachio-green (Epidote) to dark grey-green. Luster: Vitreous to pearly. Crystal structure: Monoclinic, though these are tumbled. Specific gravity: 3.3–3.5.
- Hardness
- 6–7 on Mohs scale
- Color
- Pistachio-green (Epidote) to dark grey-green
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6–7 on Mohs scale. Color: Pistachio-green (Epidote) to dark grey-green. Luster: Vitreous to pearly. Crystal structure: Monoclinic, though these are tumbled. Specific gravity: 3.3–3.5.
Formation & geological history
Formed through regional metamorphism of calcium-rich rocks or hydrothermal alteration of igneous rocks like granite or basalt. Found in rocks dating from various geological eras, often in metamorphic belts.
Uses & applications
Used primarily as decorative lapidary material, tumbled stones for collectors, and semi-precious gemstones in jewelry. Also used as a minor component in some abrasive industrial processes.
Geological facts
Epidote is named from the Greek 'epidosis' meaning 'increase,' referring to one side of the prism being longer than the other. The specific pistachio-green color is diagnostic of iron-rich epidote.
Field identification & locations
Identify in the field by its distinct yellow-green 'pistachio' color and its association with altered igneous rocks. Tumbled specimens like these are common in the Blue Ridge Mountains of the USA and in South Africa.
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