igneous
Basalt
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None (conchoidal or irregular fracture); Specific Gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None (conchoidal or irregular fracture); 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 moon. Occurs primarily at mid-ocean ridges and hotspots.
Uses & applications
Widely used in construction for aggregate, road base, concrete, and asphalt; also used for stone wool insulation and occasionally as decorative pavers.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identify by its heavy weight, dark color, and lack of visible crystals without a hand lens. Commonly found in volcanic regions, oceanic islands (like Hawaii), and Pacific Northwest plateaus.
