igneous
Basalt
Basalt (primarily composed of Plagioclase feldspar and Pyroxene)
Hardness: 6 on Mohs scale. Color: dark grey to black. Luster: dull to earthy. Crystal structure: fine-grained (aphanitic), often containing microscopic crystals. Specific gravity: 2.8–3.0.
- Hardness
- 6 on Mohs scale
- Color
- dark grey to black
- Luster
- dull to earthy
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Physical properties
Hardness: 6 on Mohs scale. Color: dark grey to black. Luster: dull to earthy. Crystal structure: fine-grained (aphanitic), often containing microscopic crystals. 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 can be found in oceanic crust and volcanic regions worldwide.
Uses & applications
Extensively used in construction for aggregate in road base, concrete, and railroad ballast. Also used as dimension stone for statues and architecture, and occasionally in jewelry as 'lava rock' beads.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floors. It is also common on the Moon and Mars—the dark 'seas' on the Moon (Maria) are actually giant basaltic plains.
Field identification & locations
Identify in the field by its dark color, heavy weight (high density), and fine-grained texture with no visible large crystals. It often breaks with a conchoidal fracture. Commonly found in volcanic fields or near coastal areas with ancient lava flows.
