igneous
Basalt
Basalt
Hardness: 6 (Mohs scale). Color: Dark gray to black, often weathering to greenish or brown. Luster: Dull to sub-metallic. Crystal structure: Aphanitic (fine-grained), sometimes vesicular or porphyritic. Specific gravity: 2.8 - 3.0. Composition: Plagioclase feldspar and pyroxene.
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray to black, often weathering to greenish or brown
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs scale). Color: Dark gray to black, often weathering to greenish or brown. Luster: Dull to sub-metallic. Crystal structure: Aphanitic (fine-grained), sometimes vesicular or porphyritic. Specific gravity: 2.8 - 3.0. Composition: Plagioclase feldspar and pyroxene.
Formation & geological history
Basalt is an extrusive volcanic rock 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 rock type in Earth's crust.
Uses & applications
Extensively used in construction for aggregate, road base, concrete, and railroad ballast. Historically used in sculpting and as a decorative stone. Crushed basalt is even used for carbon sequestration experiments.
Geological facts
Basalt makes up most of the ocean floor and is also prevalent on Mars and the Moon (the dark lunar maria are basaltic lava flows). It is the most common rock on Earth's surface.
Field identification & locations
Identify by its heavy weight (density), fine-grained texture, and dark color. It often forms hexagonal pillars known as columnar jointing in large flows. Found globally in volcanic regions and oceanic crust.
