igneous
Basalt
Mafic Igneous Rock (composed primarily of plagioclase feldspar and pyroxene)
Hardness: 6.0; Color: Dark grey to black; Luster: Dull/Sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull/Sub-metallic
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Physical properties
Hardness: 6.0; Color: Dark grey to black; Luster: Dull/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 exposed at or very near the surface of a terrestrial planet or a moon. Most basalt flows are Cenozoic in age, though it has formed throughout Earth's history.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and ground-up for mineral wool insulation. Polished slabs are used for countertops and floor tiles.
Geological facts
Basalt is the most common rock type in Earth's crust; it also makes up most of the seafloor and the lunar maria (dark plains on the Moon).
Field identification & locations
Identify by its dark color, heavy weight (density), and lack of visible crystals to the naked eye. Commonly found in volcanic regions, oceanic islands, and mid-ocean ridges.
