metamorphic
Greenschist / Serpentinite Cobble
Greenschist (composed primarily of chlorite, actinolite, and epidote)
Hardness: 3.5 - 6 on Mohs scale depending on specific mineral ratios. Color: Light grayish-green to dusty olive green. Luster: Dull to pearly or waxy. Texture: Fine-grained, slightly foliated or massive river-worn cobble. Specific gravity: 2.7 - 3.0.
- Hardness
- 3
- Color
- Light grayish-green to dusty olive green
- Luster
- Dull to pearly or waxy
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Physical properties
Hardness: 3.5 - 6 on Mohs scale depending on specific mineral ratios. Color: Light grayish-green to dusty olive green. Luster: Dull to pearly or waxy. Texture: Fine-grained, slightly foliated or massive river-worn cobble. Specific gravity: 2.7 - 3.0.
Formation & geological history
Formed via low-grade regional metamorphism of mafic igneous rocks (such as basalt or gabbro) under low temperatures and moderate pressures, typical of subduction zones and mountain-building events.
Uses & applications
Used extensively in landscaping as decorative river rocks, crushed stone for road construction, and occasionally for carving or stone masonry.
Geological facts
Greenschist gets its characteristic greenish color from green metamorphic minerals like chlorite, epidote, and actinolite. River-worn specimens like this one have been smoothed by natural water transport over thousands of years.
Field identification & locations
Identify in the field by its distinct greenish-gray cast, fine texture, and smooth rounded river-cobble shape. Extremely common in riverbeds draining metamorphic mountain ranges such as the Coast Ranges and Sierra Nevada in California.
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