igneous
Basalt
Mafic volcanic rock (primarily plagioclase feldspar and pyroxene)
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None; Specific gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None; 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 common in oceanic crust and volcanic hotspots.
Uses & applications
Extensively used in construction as aggregate for road base, railroad ballast, and concrete. Also used for high-quality floor tiles and stonework in landscaping.
Geological facts
Basalt is the most abundant bedrock on Earth, making up the vast majority of the ocean floor. It is cũng the primary rock type on the Moon's Maria and large portions of Mars and Venus.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often shows vesiculation (small air bubbles). Common in regions like the Pacific Northwest, Hawaii, and Iceland.
