igneous
Basalt
Basalt (principally Plagioclase Feldspar and Pyroxene)
Hardness: 6; Color: Black, dark gray, or charcoal; Luster: Dull to sub-metallic (when fresh); Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0
- Hardness
- 6
- Color
- Black, dark gray, or charcoal
- Luster
- Dull to sub-metallic (when fresh)
Identified More igneous →
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Physical properties
Hardness: 6; Color: Black, dark gray, or charcoal; Luster: Dull to sub-metallic (when fresh); 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 at or very near the Earth's surface. Common in oceanic crust and volcanic regions.
Uses & applications
Used widely in construction as crushed stone for road base, railroad ballast, and concrete aggregate; also used for stone wool insulation and cobblestones.
Geological facts
Basalt is the most common rock type in the Earth's crust and covers most of the ocean floor. It is also found on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and very fine-grained texture. Found near volcanic hotspots, mid-ocean ridges, and island arcs.
