igneous
Basalt
Mafic Igneous Basalt
Hardness: 6 on Mohs scale; Color: Dark grey to black, sometimes weathering to brown; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic), sometimes vesicular; Cleavage: None (conchoidal fracture).
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black, sometimes weathering to brown
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black, sometimes weathering to brown; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic), sometimes vesicular; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Common in oceanic crust and volcanic regions.
Uses & applications
Extensively used in construction for aggregate, road base, concrete, and railroad ballast. Also used as dimension stone for pavement and monuments.
Geological facts
Basalt is the most common rock type on the Earth's surface and also covers large areas of the Moon, Mars, and Venus, known as 'maria' on the Moon.
Field identification & locations
Identify by its dark color, heavy weight (high density), and fine grain that is usually too small to see with the naked eye. Found in volcanic terrain or riverbeds near volcanic sources.
