metamorphic
Greenstone
Metamorphic mafic rock (greenschist facies)
Hardness: 5-6 on the Mohs scale, Color: Green, grayish-green, or dark green, Luster: Dull to sub-vitreous, Crystal structure: Microcrystalline to fine-grained, Cleavage: Poor to none, Specific Gravity: 2.7-3.0
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Physical properties
Hardness: 5-6 on the Mohs scale, Color: Green, grayish-green, or dark green, Luster: Dull to sub-vitreous, Crystal structure: Microcrystalline to fine-grained, Cleavage: Poor to none, Specific Gravity: 2.7-3.0
Formation & geological history
Formed through low-grade regional metamorphism of mafic igneous rocks such as basalt, gabbro, or diabase, typically under temperatures of 300-450 degrees Celsius and moderate pressures in ancient orogenic belts.
Uses & applications
Historically used by indigenous peoples for making polished stone axes and adzes; occasionally used as a decorative stone or lapidary material.
Geological facts
The characteristic green color comes from minerals like chlorite, epidote, and actinolite that form during the metamorphic alteration of original pyroxenes and calcic plagioclase.
Field identification & locations
Identified in the field by its distinct greenish hue and fine-grained texture; commonly found in ancient shield areas, greenstone belts, and mountain building zones worldwide.
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