metamorphic
Greenstone (Greenstone River Pebble)
Greenschist (metamorphosed mafic igneous rock)
Hardness: 3.5-5 (Mohs scale); Color: Dull green, gray-green, or olive; Luster: Sub-vitreous to waxy; Structure: Finely crystalline to foliated; Cleavage: Poor; Specific Gravity: 2.8-3.0
- Hardness
- 3
- Color
- Dull green, gray-green, or olive
- Luster
- Sub-vitreous to waxy
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Physical properties
Hardness: 3.5-5 (Mohs scale); Color: Dull green, gray-green, or olive; Luster: Sub-vitreous to waxy; Structure: Finely crystalline to foliated; Cleavage: Poor; Specific Gravity: 2.8-3.0
Formation & geological history
Formed through low-grade metamorphism (high pressure, low temperature) of basaltic or gabbroic rocks. Often associated with ancient subduction zones and mountain-building events (Orogeny).
Uses & applications
Used historically for stone tools (axes, adzes) due to toughness; modern uses include landscaping stones, aquarium decor, and occasionally as a minor semi-precious craving stone.
Geological facts
The green color is primarily due to the presence of minerals like chlorite, epidote, and actinolite. In New Zealand, a specific high-quality variety known as Pounamu is culturally sacred to the Māori people.
Field identification & locations
Identify by its characteristic 'sea-foam' or dull green hue and smooth, rounded water-worn texture if found near rivers. It is often heavier than it looks. Commonly found in riverbeds near tectonic plate boundaries (e.g., California, Washington, New Zealand).
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