metamorphic
Greenstone / Greenschist
Greenschist facies metamorphic rock
Hardness: 3.5-5.5 (variable); Color: Dull green, grayish-green; Luster: Sub-vitreous to earthy; Texture: Fine-grained, often foliated or massive; Specific Gravity: 2.8-3.0. Common minerals include chlorite, actinolite, and epidote.
- Hardness
- 3
- Color
- Dull green, grayish-green
- Luster
- Sub-vitreous to earthy
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Physical properties
Hardness: 3.5-5.5 (variable); Color: Dull green, grayish-green; Luster: Sub-vitreous to earthy; Texture: Fine-grained, often foliated or massive; Specific Gravity: 2.8-3.0. Common minerals include chlorite, actinolite, and epidote.
Formation & geological history
Formed by low-grade regional metamorphism of mafic igneous rocks (such as basalt) under low temperatures and pressures, typically within subduction zones or mountain-building environments.
Uses & applications
Historically used for stone tools (axes), construction material, road ballast, and occasionally for decorative stone carvings.
Geological facts
The green color is primarily due to the presence of chlorite minerals. Often referred to as 'greenstone' by archaeologists when found as ancient tools.
Field identification & locations
Identify in the field by its distinct greenish hue and fine-grained texture. Commonly found in metamorphic belts like the Appalachians or the Scottish Highlands. Look for a dense, tough feel compared to sedimentary rocks.
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