igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6-7 Mohs; Color: dark grey to black; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic) or porphyritic; Specific gravity: 2.8 to 3.0. Dense and heavy for its size.
- Hardness
- 6-7 Mohs
- Color
- dark grey to black
- Luster
- dull to sub-metallic
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Physical properties
Hardness: 6-7 Mohs; Color: dark grey to black; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic) or porphyritic; Specific gravity: 2.8 to 3.0. Dense and heavy for its size.
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, primarily forming the ocean floor.
Uses & applications
Extensively used in construction for aggregate, road base, and railroad ballast. In industry, it can be melted into stone wool for insulation. High-density specimens are used for river stone massage and landscaping decoration.
Geological facts
Basalt is the most common rock type on the surfaces of Mars and the Moon (Lunar Maria). It famously forms unique hexagonal columns at the Giant's Causeway in Ireland and Devil's Postpile in California.
Field identification & locations
Identify in the field by its dark, uniform color, fine grain, and heaviness. It often has small 'vesicles' (bubbles) from trapped gas. Commonly found in volcanic regions and ocean shorelines.
