igneous
Basalt
Basalt
Hardness: 6.0–7.0 Mohs; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6.0–7.0 Mohs; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained); 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. Most basalt on Earth is formed at mid-ocean ridges.
Uses & applications
Used extensively in construction as crushed stone for road base, railroad ballast, and concrete aggregate. High-quality specimens are used in stone masonry and as basalt fiber for reinforcement.
Geological facts
Basalt is the most common rock type in the Earth's crust and covers most of the ocean floor. It is also found extensively on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (density), and lack of visible crystals to the naked eye. Often found in volcanic regions or as worn pebbles in riverbeds.
