igneous
Basalt Pebble
Basalt
Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull or earthy; Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0
- Hardness
- 6-7 Mohs
- Color
- Dark grey to black
- Luster
- Dull or earthy
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull or earthy; Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. Most common rock in Earth's crust.
Uses & applications
Used in construction as aggregate, for paving, in the production of stone wool insulation, and as tumbled decorative stones.
Geological facts
Basalt makes up most of the ocean floor and is also prevalent on Mars and the Moon (the dark lunar maria are basaltic lava plains).
Field identification & locations
Identify by its dark color, heavy weight for its size, and fine-grained texture lacking visible crystals. Often found as rounded pebbles on beaches or in riverbeds downstream from volcanic sources.
