Igneous
Basalt
Mafic volcanic rock (Primarily Plagioclase Feldspar and Pyroxene)
Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0.
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray to black
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark gray 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. Common in oceanic crust and continental flood basalts.
Uses & applications
Extensively used in construction as crushed stone for road base, railroad ballast, and concrete aggregate; also used for high-durability floor tiles and garden landscaping.
Geological facts
Basalt is the most common rock type in the Earth's crust and also makes up most of the surface of the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and lack of visible large crystals. It often has sharp edges when freshly broken (conchoidal fracture). Common in volcanic regions.
