igneous
Basalt
Basalt
Hardness: 6-7 on Mohs scale; Color: Dark grey to black, often weathering to brown/green; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0
- Hardness
- 6-7 on Mohs scale
- Color
- Dark grey to black, often weathering to brown/green
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark grey to black, often weathering to brown/green; Luster: Dull to sub-metallic; Crystal 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. It is the most common volcanic rock on Earth.
Uses & applications
Extensively used in construction for road base, concrete aggregate, railroad ballast, and as a raw material for stone wool insulation.
Geological facts
Basalt underlies more of Earth's surface than any other rock type; most areas within Earth's ocean basins are underlain by basalt. It also makes up large portions of the Moon's surface.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and lack of visible large crystal grains without a lens. Found globally in volcanic regions and ocean floor crust.
