igneous
Basalt
Basalt
Hardness: 6 on Mohs scale; Color: Dark grey to black, weathering to brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Density: 2.9-3.1 g/cm³
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black, weathering to brown
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black, weathering to brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Density: 2.9-3.1 g/cm³
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, especially as crushed stone for road base, concrete aggregate, and railroad ballast. Also used as a dimension stone for flooring and monuments.
Geological facts
Basalt makes up most of the world's ocean floor. It is also found on the Moon and Mars, where the dark 'maria' (seas) are ancient basaltic lava flows.
Field identification & locations
Identified in the field by its dark color, heavy weight, and fine-grained texture. It often shows vesiculation (small holes from gas bubbles) or columnar jointing. Commonly found in volcanic island chains and oceanic crust.
