igneous
Basalt Pebble
Extrusive Igneous Rock (Mafic)
Hardness: 6 on the Mohs scale. Color: Dark gray to black. Luster: Dull to sub-vitreous. Crystal structure: Aphanitic (fine-grained), often containing microscopic minerals like plagioclase feldspar, pyroxene, and olivine. Specific gravity: 2.8 - 3.0.
- Hardness
- 6 on the Mohs scale
- Color
- Dark gray to black
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on the Mohs scale. Color: Dark gray to black. Luster: Dull to sub-vitreous. Crystal structure: Aphanitic (fine-grained), often containing microscopic minerals like plagioclase feldspar, pyroxene, and olivine. Specific gravity: 2.8 - 3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity, magnesium- and iron-rich lava exposed at or very near the Earth's surface, typically from volcanic eruptions. Geological age ranges from recent volcanic activity to billions of years old.
Uses & applications
Used widely in construction as crushed stone for road bases, aggregate in concrete, railroad ballast, and sometimes in countertops and landscaping.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's ocean basins, and it is also the primary volcanic rock found on the Moon (forming the lunar maria) and Mars.
Field identification & locations
Easily identified by its dark gray to black coloration and fine-grained, heavy texture. Often found smoothed and rounded along beaches, rivers, and glacial deposits due to wave or water action.
