metamorphic
Greenstone
Epidiorite / Altered Basalt
Hardness: 6-6.5 (Mohs scale), Color: Dull forest green to grey-green, Luster: Dull to waxy, Structure: Fine-grained/Aphanitic, Cleavage: None (conchoidal fracture), Specific Gravity: 2.85-3.0
- Hardness
- 6-6
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Physical properties
Hardness: 6-6.5 (Mohs scale), Color: Dull forest green to grey-green, Luster: Dull to waxy, Structure: Fine-grained/Aphanitic, Cleavage: None (conchoidal fracture), Specific Gravity: 2.85-3.0
Formation & geological history
Formed through the low-grade metamorphism of mafic igneous rocks (like basalt or gabbro) under relatively low temperature and pressure conditions, often in subduction zones or seafloor hydrothermal environments.
Uses & applications
Historically used for making stone tools/axes due to its toughness; currently used as crushed stone in construction, for lapidary work, and landscaping.
Geological facts
The term 'greenstone' refers to the green minerals produced during metamorphism, such as chlorite, actinolite, and epidote. Ancient civilizations preferred it for 'celt' axes because it does not shatter easily on impact.
Field identification & locations
Identify in the field by its distinct dull green color and lack of visible crystals. It is much harder than shale and won't scratch with a steel knife. Commonly found in ancient volcanic belts and mountain ranges.
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