igneous
Basalt
Extrusive Igneous Basalt
Hardness: 5-6 Mohs. Color: Dark gray to black. Luster: Dull/Matte. Crystal structure: Aphanitic (fine-grained), often containing plagioclase feldspar and pyroxene. Specific gravity: 2.8–3.0.
- Hardness
- 5-6 Mohs
- Color
- Dark gray to black
- Luster
- Dull/Matte
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Physical properties
Hardness: 5-6 Mohs. Color: Dark gray to black. Luster: Dull/Matte. Crystal structure: Aphanitic (fine-grained), often containing plagioclase feldspar and pyroxene. 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 on Earth was formed by volcanic activity at mid-ocean ridges.
Uses & applications
Commonly used in construction as aggregate for roads, railroad ballast, and concrete. It is also used as dimension stone for pavings and in statue carving.
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 in the field by its dark color, heavy weight (density), and fine-grained texture. It often shows columnar jointing or vesicular (pitted) surfaces if gases were trapped during cooling.
