igneous
Basalt
Basalt
Hardness: 6.0; 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
Identified More igneous →
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Physical properties
Hardness: 6.0; 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 at or very near the Earth's surface. Basalt is the most common rock type in the Earth's crust (especially oceanic crust).
Uses & applications
Used primarily as crushed stone for road base, railroad ballast, and concrete aggregate. Some denser varieties are used for floor tiles and statues.
Geological facts
Basalt also makes up most of the ocean floor and is found on other planetary bodies like the Moon (lunar maria) and Mars.
Field identification & locations
Identify by its dark color, fine grain, and weight (heavier than most rocks of similar size due to iron content). Common in volcanic regions like Hawaii or the Pacific Northwest.
