metamorphic
Greenstone / Greenschist
Chlorite schist / Meta-basalt
Hardness: 3-5 (Mohs scale); Color: Dull green, grayish-green with white quartz veins; Luster: Sub-vitreous to earthy; Structure: Foliated to massive; Cleavage: Often present in schistose varieties; Specific gravity: 2.7-3.2.
- Hardness
- 3-5 (Mohs scale)
- Color
- Dull green, grayish-green with white quartz veins
- Luster
- Sub-vitreous to earthy
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Physical properties
Hardness: 3-5 (Mohs scale); Color: Dull green, grayish-green with white quartz veins; Luster: Sub-vitreous to earthy; Structure: Foliated to massive; Cleavage: Often present in schistose varieties; Specific gravity: 2.7-3.2.
Formation & geological history
Formed through regional metamorphism of mafic igneous rocks (like basalt or gabbro) under low temperatures and moderate pressure (greenschist facies). This process often occurs at subduction zones or mountain-building events.
Uses & applications
Used historically for axes and tools; currently used as construction aggregate, decorative garden stone, and occasionally for carving.
Geological facts
The characteristic green color comes from minerals like chlorite, epidote, and actinolite. Some greenstones represent ancient oceanic crust that was thrusted onto continental margins.
Field identification & locations
Identify by its distinctive grayish-green hue and the presence of white quartz or calcite veins. It is commonly found in ancient mountain belts like the Appalachians or the Scottish Highlands.
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