igneous
Basalt Pebble
Aphanitic Mafic Igneous Rock
Hardness: 6 on the Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Microcrystalline or cryptocrystalline; Cleavage: None; Specific Gravity: 2.8 - 3.0
- Hardness
- 6 on the Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on the Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Microcrystalline or cryptocrystalline; Cleavage: None; 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 surface of a rocky planet or moon. Geological age varies widely from recent volcanic eruptions to billions of years old.
Uses & applications
Commonly used in construction as crushed stone for road bases, railroad ballast, concrete aggregate, and in landscaping or decorative gravel.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the ocean basins, and it is also extensively found on the Moon, Mars, and Venus.
Field identification & locations
Easily identified by its dark grey to black color, fine-grained (aphanitic) texture where individual crystals are not visible to the naked eye, and high density. Found worldwide in volcanic regions and riverbeds where weathering creates smooth pebbles.
