igneous
Basalt River Pebble
Basalt (Mafic Volcanic Rock)
Hardness: 6.0 on Mohs scale; Color: Dark grey to charcoal; Luster: Dull/matt when dry; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific Gravity: 2.8-3.0
- Hardness
- 6
- Color
- Dark grey to charcoal
- Luster
- Dull/matt when dry
Identified More igneous →
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Physical properties
Hardness: 6.0 on Mohs scale; Color: Dark grey to charcoal; Luster: Dull/matt when dry; Crystal structure: Aphanitic (fine-grained); Cleavage: None; 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 smooth-rounded by water erosion in a river or coastal environment.
Uses & applications
Used extensively in construction as crushed stone for road bases and concrete; also popular in landscaping, aquarium decor, and massage therapy (hot stones).
Geological facts
Basalt is the most common rock type in the Earth's crust and covers most of the ocean floor. It also makes up the lunar maria on the Moon.
Field identification & locations
Identified by its heavy weight (density), dark uniform color, and fine-grained texture. Commonly found in volcanic regions, riverbeds, and beaches across the Pacific Northwest and Hawaii.
