igneous
Basalt
Aphanitic Mafic Igneous Rock
Hardness: 6.0 on Mohs scale; Color: black to dark gray; Luster: dull to sub-vitreous (when polished); Crystal Structure: fine-grained (aphanitic) or glassy; Specific Gravity: 2.8 - 3.0.
- Hardness
- 6
- Color
- black to dark gray
- Luster
- dull to sub-vitreous (when polished)
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Physical properties
Hardness: 6.0 on Mohs scale; Color: black to dark gray; Luster: dull to sub-vitreous (when polished); Crystal Structure: fine-grained (aphanitic) or glassy; 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 is the most common volcanic rock on Earth.
Uses & applications
Basalt is used in construction (crushed stone for road base and railroad ballast), for making stone wool (insulation material), and polished specimens are used as massage stones or decorative pebbles.
Geological facts
Basalt underlies more of Earth's surface than any other rock type. Most of the ocean floor is basalt. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size), and fine-grained texture with no visible crystals. Often found in volcanic regions or alongside riverbeds as water-worn cobbles.
