igneous
Basalt (Crushed Stone)
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6-7 Mohs; Color: Dark grey to black, weathering to brown; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0
- Hardness
- 6-7 Mohs
- Color
- Dark grey to black, weathering to brown
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to black, weathering to brown; Luster: Dull/Earthy; 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. This specimen appears to be mechanically crushed aggregate, most likely from the Cenozoic era or older volcanic flows.
Uses & applications
Extensively used in construction for road base, concrete aggregate, asphalt pavement, and railroad ballast. Also used in architectural stone and high-temperature insulation (capping stone).
Geological facts
Basalt is the most common rock type in Earth's crust and makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and fine-grained texture that lacks visible crystals to the naked eye. Commonly found in quarries and near volcanic regions.
