igneous
Basalt
Basalt
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained); Cleavage: None/conchoidal; Specific Gravity: 2.8-3.0.
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained); Cleavage: None/conchoidal; 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 was formed during the Cenozoic and Mesozoic eras.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and ground-stone high-performance concrete. Occasionally used in stone carvings and as a heat source in 'hot stone' therapy.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It also exists on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (density), and fine-grained texture that lacks visible crystals. Commonly found along mid-ocean ridges and volcanic islands. In the field, look for 'columnar jointing' or smooth, water-worn pebbles in riverbeds.
