igneous
Stream Pebble (Basalt/Greywacke)
Mafic Igneous Rock (Fine-grained)
Hardness: 5-7 Mohs; Color: dark grey to black with green/brown weathering; Luster: dull to earthy; Texture: aphanitic to fine-grained; Specific Gravity: 2.8-3.0
- Hardness
- 5-7 Mohs
- Color
- dark grey to black with green/brown weathering
- Luster
- dull to earthy
Identified More igneous →
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Physical properties
Hardness: 5-7 Mohs; Color: dark grey to black with green/brown weathering; Luster: dull to earthy; Texture: aphanitic to fine-grained; Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. This specific specimen has been rounded by mechanical weathering in a river or stream environment.
Uses & applications
Common river stones are used for decorative landscaping, construction aggregate, and ground cover. High-density varieties are sometimes used for hot stone massage therapy.
Geological facts
River pebbles like this one can travel hundreds of miles from their source rock, becoming smoother and more spherical as they collide with other rocks in the water current.
Field identification & locations
Identify by its water-worn, smooth surface, heavy weight for its size, and lack of visible large crystals. Often found in current or ancient riverbeds and coastal areas.
