metamorphic
Greenstone
Greenschist (Greened Metabasalt)
Hardness: 5-7 (Mohs scale), Color: Dull green, grayish-green, with possible white quartz or calcite veins, Luster: Dull to waxy, Crystal Structure: Microcrystalline, Cleavage: Poor to none (massive), Specific Gravity: 2.8-3.3
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Physical properties
Hardness: 5-7 (Mohs scale), Color: Dull green, grayish-green, with possible white quartz or calcite veins, Luster: Dull to waxy, Crystal Structure: Microcrystalline, Cleavage: Poor to none (massive), Specific Gravity: 2.8-3.3
Formation & geological history
Formed through low-grade metamorphism of mafic igneous rocks (like basalt) under temperatures of 300 to 450 degrees Celsius and moderate pressure, often in subduction zones or mountain-building regions.
Uses & applications
Used historically for stone tools and weapons (axes); currently used as crushed stone for road construction, decorative garden stone, and occasionally for sculpting.
Geological facts
The green color is primarily due to the presence of chlorite, epidote, or actinolite minerals formed during the metamorphic process. It is a key indicator rock for geologists studying ancient plate tectonics.
Field identification & locations
Identify by its distinctive dull green hue and find it in regions of ancient volcanic activity. Collectors looks for smooth, river-worn specimens or those with interesting mineral inclusions.
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