metamorphic
Greenstone (or River-tumbled Basalt / Greywacke with Epidote)
Metabasalt / Greenschist facies rock
Hardness: 5.5-6.5 on Mohs scale. Color: Muted sage to olive green with fine speckling. Luster: Dull to sub-vitreous. Texture: Very smooth, water-worn beach/river pebble. Density: Medium to high specific gravity (around 2.8-3.0).
- Hardness
- 5
- Color
- Muted sage to olive green with fine speckling
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 5.5-6.5 on Mohs scale. Color: Muted sage to olive green with fine speckling. Luster: Dull to sub-vitreous. Texture: Very smooth, water-worn beach/river pebble. Density: Medium to high specific gravity (around 2.8-3.0).
Formation & geological history
Formed from low-grade regional or hydrothermal metamorphism of mafic volcanic rocks (such as basalt). Minerals like epidote, chlorite, and actinolite impart the characteristic greenish hue. Naturally rounded and smoothed by fluid abrasion in rivers or ocean waves.
Uses & applications
Commonly collected as river rocks, landscaping pebbles, decorative beach stones, and for lapidary tumbling or cabochon carving.
Geological facts
Greenstone is a broad term used for altered mafic igneous rocks. In ancient times, indigenous peoples worldwide used dense greenstones to craft polished stone axes, adzes, and ornamental objects due to their toughness and resistance to fracturing.
Field identification & locations
Identified by its fine-grained texture, pale olive-green color, and high toughness. Frequently found along Pacific Northwest beaches, gravel bars, and riverbeds. Very common rock with minimal monetary value, typically gathered for personal collections.
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