igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6; Color: Dark grey to black; Luster: Dull to sub-metallic when wet; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.9-3.1
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic when wet
Identified More igneous →
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Physical properties
Hardness: 6; Color: Dark grey to black; Luster: Dull to sub-metallic when wet; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.9-3.1
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the surface of a terrestrial planet or the moon. Most specimens date from various volcanic episodes throughout Earth's history.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and paving stones. High-quality dense basalt is also used for stone carving and as a thermal insulator in the form of rock wool.
Geological facts
Basalt is the most common rock type in 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 for its size (density), and lack of visible large crystals. Common in volcanic regions, riverbeds near volcanic plateaus, and coastal areas.
