igneous
Basalt
Basalt (primarily Plagioclase feldspar and Pyroxene)
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to submetallic; Crystal structure: Aphanitic (fine-grained); Cleavage: Poor; Specific gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull to submetallic
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to submetallic; Crystal structure: Aphanitic (fine-grained); Cleavage: Poor; 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. It can be from any geological age, commonly Cenozoic.
Uses & applications
Used extensively in construction as road base, railroad ballast, and concrete aggregate. Some varieties are used in stonewalling and as a material for thermal insulation (rock wool).
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floors. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identify by its dark color, heavy weight (density), and lack of visible crystals to the naked eye. It can often be found in volcanic regions or as glacial erratics.
