igneous
Basalt Pebble
Extrusive Igneous Rock
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), often containing microscopic olivine, pyroxene, and plagioclase; Specific gravity: 2.8 - 3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), often containing microscopic olivine, pyroxene, and plagioclase; Specific gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron exposed at or very near the surface of a planet or moon.
Uses & applications
Used in construction as crushed stone for aggregate, railroad ballast, road base, and in the manufacture of stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the ocean basins and forms much of the volcanic islands worldwide as well as the dark maria on the Moon.
Field identification & locations
Easily identified by its dark grey to black color, fine-grained texture, and smooth, water-worn shape when found in riverbeds or beaches. Common worldwide.
