igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull/Sub-metallic; Structure: Fine-grained/Aphanitic; Specific Gravity: 2.8–3.0
- Hardness
- 6-7 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull/Sub-metallic
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull/Sub-metallic; Structure: Fine-grained/Aphanitic; Specific Gravity: 2.8–3.0
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 mid-ocean ridges.
Uses & applications
Used extensively in construction as road base, railroad ballast, concrete aggregate, and as a raw material for stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust and also makes up the lunar maria on the Moon. It frequently forms impressive columnar joints.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and very fine grains. Can be found in volcanic regions, along coastlines with volcanic history, or in riverbeds downstream from volcanic mountains.
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