igneous
Basalt River Stone
Basalt (extrusive igneous rock)
Hardness: 5-6 Mohs. Color: Black to dark gray. Luster: Dull to sub-vitreous. Crystal structure: Aphanitic (fine-grained) to porphyritic. Specific gravity: 2.8–3.0. Texture: Smooth and rounded due to water erosion.
- Hardness
- 5-6 Mohs
- Color
- Black to dark gray
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 5-6 Mohs. Color: Black to dark gray. Luster: Dull to sub-vitreous. Crystal structure: Aphanitic (fine-grained) to porphyritic. Specific gravity: 2.8–3.0. Texture: Smooth and rounded due to water erosion.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This specific specimen has been rounded through fluvial (river) or coastal erosion over centuries.
Uses & applications
Used extensively in construction as aggregate, in 'hot stone' massage therapy for heat retention, and as decorative landscaping stones.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon and Mars.
Field identification & locations
Identified in the field by its dark color, heavy weight (density), and fine-grained texture. Commonly found in riverbeds and on beaches in volcanic regions.
