metamorphic
Greenstone (Metabalt)
Chlorite schist / Epidiorite
Hardness: 5-7. Color: Dull grayish-green. Luster: Dull or earthy. Structure: Fine-grained, massive to slightly foliated. Contains minerals like chlorite, epidote, and actinolite.
- Hardness
- 5-7
- Color
- Dull grayish-green
- Luster
- Dull or earthy
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Physical properties
Hardness: 5-7. Color: Dull grayish-green. Luster: Dull or earthy. Structure: Fine-grained, massive to slightly foliated. Contains minerals like chlorite, epidote, and actinolite.
Formation & geological history
Formed through low-grade regional metamorphism of mafic igneous rocks (like basalt) under high pressure and low heat, often in orogenic (mountain-building) belts.
Uses & applications
Used historically as a material for stone tools (axes), in modern times as decorative garden stone, crushed stone for road construction, and occasionally for architectural facing.
Geological facts
The characteristic green color comes from chlorite and epidote minerals. It was a prized material in the Neolithic era for creating 'polished stone axes' because of its toughness and ability to take a sharp edge.
Field identification & locations
Identify by its distinctive dull green hue and lack of visible crystals. It is common in ancient mountain ranges like the Appalachians or the Scottish Highlands. It feels denser and heavier than similarly colored sedimentary rocks.
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