metamorphic
Greenstone (Epidosite/Altered Diorite)
Metabasalt or Meta-andesite / Epidotized Diorite
Hardness: 6-7 Mohs; Color: Dull green, olive to sage green with white/pinkish plagioclase flecks and dark hornblende; Luster: Dull to waxy; Texture: Fine to medium-grained; Cleavage: Poor
- Hardness
- 6-7 Mohs
- Luster
- Dull to waxy
Identified More metamorphic →
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Physical properties
Hardness: 6-7 Mohs; Color: Dull green, olive to sage green with white/pinkish plagioclase flecks and dark hornblende; Luster: Dull to waxy; Texture: Fine to medium-grained; Cleavage: Poor
Formation & geological history
Formed through low-grade regional metamorphism (greenschist facies) of mafic to intermediate igneous rocks. The green color comes from the alteration of minerals to epidote, chlorite, and actinolite.
Uses & applications
Primarily used as river rock for landscaping, decorative gravel, or in road construction. Some high-quality specimens are used in lapidary for polishing or carving.
Geological facts
Greenstone is a general field term for any dark, greenish-colored altered igneous rock. It is a major component of 'Greenstone Belts' which contain some of Earth's oldest rocks and significant gold deposits.
Field identification & locations
Commonly found in riverbeds and glacial tills. Identify by its distinct greenish hue that remains even when dry, and its high hardness (won't be scratched by a steel knife). Commonly found in the Pacific Northwest and Great Lakes regions.
