metamorphic
Greenstone / Greenstone Pebble
Greenschist (metamorphosed basalt or gabbro)
Hardness: 5-6 (Mohs); Color: Dark green to grayish-green; Luster: Dull to waxy; Texture: Fine-grained, dense; Composition: Chlorite, epidote, and actinolite; Specific gravity: ~2.8-3.0.
- Hardness
- 5-6 (Mohs)
- Color
- Dark green to grayish-green
- Luster
- Dull to waxy
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark green to grayish-green; Luster: Dull to waxy; Texture: Fine-grained, dense; Composition: Chlorite, epidote, and actinolite; Specific gravity: ~2.8-3.0.
Formation & geological history
Formed through regional metamorphism of mafic igneous rocks (like basalt) under low-temperature, moderate-pressure conditions. Often associated with ancient subduction zones and mountain-building events.
Uses & applications
Historically used for making stone tools (axes and adzes) due to its toughness; currently used as decorative gravel, in landscaping, and as a collector's specimen.
Geological facts
The green color is primarily due to the presence of chlorite and epidote minerals. In some regions, like New Zealand, specific types of high-grade greenstone (Pounamu) are culturally sacred and highly valuable.
Field identification & locations
Identify by its distinct greenish hue and lack of visible crystals. It is much tougher than many other river rocks. Commonly found in areas with ancient volcanic activity or along pebbly beaches near metamorphic belts.
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