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 crystals or volcanic glass. 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 crystals or volcanic glass. 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, often in volcanic environments or ocean floors.
Uses & applications
Used in construction as crushed stone for road bases, concrete aggregate, and railroad ballast, as well as in stonemasonry and countertops.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the oceans, and it is also found extensively on the Moon (making up the lunar maria) and Mars.
Field identification & locations
Identify in the field by its dark, dense, fine-grained appearance, often smoothed and rounded into pebbles by water action in rivers or shorelines. Found worldwide.
