metamorphic
Greenstone (Epidote/Chlorite Rich Rock)
Metabasalt (often contains Epidote Ca2Al2(Fe3+;Al)(SiO4)(Si2O7)O(OH))
Hardness: 6-7 on Mohs scale; Color: Variable shades of forest green to olive; Luster: Dull to greasy; Structure: Massive to slightly foliated; Specific Gravity: 2.9–3.3.
- Hardness
- 6-7 on Mohs scale
- Color
- Variable shades of forest green to olive
- Luster
- Dull to greasy
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Variable shades of forest green to olive; Luster: Dull to greasy; Structure: Massive to slightly foliated; Specific Gravity: 2.9–3.3.
Formation & geological history
Formed through the low-grade regional metamorphism of mafic igneous rocks (like basalt). Usually associated with Paleozoic or Proterozoic mountain-building events in subduction zones.
Uses & applications
Used primarily as crushed stone for road construction, architectural facing stone, and occasionally for lapidary work like beads or carvings if the color is vibrant.
Geological facts
The green color is derived from the presence of minerals like chlorite, actinolite, and epidote which replace the original minerals during metamorphism. Large belts of this rock are found in the Appalachian Mountains.
Field identification & locations
Identify by its distinctive greenish hue and toughness (it is harder than steel). Commonly found in riverbeds or coastal areas near ancient volcanic belts. Collectors look for 'unakite' varieties which include pink feldspar.
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