metamorphic
Greenstone
Greenschist
Hardness: 3.5-5 (Mohs scale); Color: green to gray-green; Luster: dull to silky; Crystal structure: fine-grained, foliated or schistose; Cleavage: good in one direction (slaty/schistose); Specific gravity: 2.8-3.0
- Hardness
- 3
- Color
- green to gray-green
- Luster
- dull to silky
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Physical properties
Hardness: 3.5-5 (Mohs scale); Color: green to gray-green; Luster: dull to silky; Crystal structure: fine-grained, foliated or schistose; Cleavage: good in one direction (slaty/schistose); Specific gravity: 2.8-3.0
Formation & geological history
Formed through low-grade regional metamorphism of mafic igneous rocks (like basalt or gabbro). The green color comes from minerals like chlorite, epidote, and actinolite formed under high pressure and low temperature conditions.
Uses & applications
Primarily used as aggregate in road construction, stone for decorative garden landscaping, and occasionally in jewelry as ornamental stones when polished.
Geological facts
The term 'greenstone' is often used in archaeology to describe various green-colored stones used for making artifacts like axes. Ancient Māori in New Zealand famously used a type of greenstone (Pounamu) for ceremonial tools.
Field identification & locations
Identify in the field by its distinct dull green hue and fine-grained texture. It often shows subtle layering (foliation). Common in ancient mountain belts and subduction zones. Look for light-colored veins of quartz or calcite cutting through the green matrix.
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