igneous
Basalt Pebble
Aphanitic mafic extrusive 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 Earth's surface, typically in volcanic settings or oceanic crust.
Uses & applications
Commonly used in construction, crushed stone for roadbeds, railroad ballast, and decorative landscaping stones.
Geological facts
Basalt is the most common rock type in the Earth's crust, primarily making up the ocean floors and significant volcanic regions on continents, as well as being found on the Moon and Mars.
Field identification & locations
Easily identified by its dark, fine-grained appearance, high density, and smooth, water-worn shape when found as pebbles in riverbeds or beaches.
