igneous
Basalt Pebble
Mafic Igneous Rock (Basalt/Diabase)
Hardness: 6 on Mohs scale; Color: Dark grey to black with fine-grained texture; Luster: Dull to sub-metallic; Structure: Aphanitic (fine-grained matrix); Cleavage: None (conchoidal to irregular fracture); Specific Gravity: 2.8-3.0.
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black with fine-grained texture
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black with fine-grained texture; Luster: Dull to sub-metallic; Structure: Aphanitic (fine-grained matrix); Cleavage: None (conchoidal to irregular fracture); Specific Gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Typical of volcanic oceanic crusts and flood basalt provinces.
Uses & applications
Basalt is widely used in construction as crushed stone, aggregate for concrete, asphalt paving, and railway ballast. Polished basalt pebbles are used decoratively in landscaping and aquariums.
Geological facts
Basalt is the most common rock type in the Earth's crust, making up most of the ocean floors. It is also extremely common on the Moon and Mars.
Field identification & locations
Identified by its dark coloration, heavy feel (high density), and fine-grained, non-crystalline surface texture. Commonly found along riverbeds, beaches, and volcanic terrains.
