metamorphic
Greenstone (Prase / Metavolcanic)
Metamorphosed volcanic rock (Greenstone)
Hardness generally ranges from 5 to 6 on the Mohs scale, color is characteristically mottled green due to chlorite, epidote, and actinolite, luster is dull to greasy, and it has a dense, compact crystal structure with no prominent cleavage.
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Physical properties
Hardness generally ranges from 5 to 6 on the Mohs scale, color is characteristically mottled green due to chlorite, epidote, and actinolite, luster is dull to greasy, and it has a dense, compact crystal structure with no prominent cleavage.
Formation & geological history
Formed through low-grade regional metamorphism of mafic igneous rocks such as basalt, gabbro, or diabase, typically in ancient subduction zones or greenstone belts dating from the Precambrian to younger orogenic belts.
Uses & applications
Used historically by indigenous peoples for making polished stone axes and adzes, and occasionally cut and polished as an ornamental stone, decorative aggregate, or lapidary material.
Geological facts
Greenstone belts are among the oldest rock formations on Earth, containing some of the earliest evidence of ancient tectonic activity and primitive life forms.
Field identification & locations
Easily identified in the field by its distinct greenish coloration and fine-grained, altered volcanic texture. Commonly found in glaciated regions as erratic boulders or in mountainous terrain associated with ancient volcanic arcs.
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