igneous
Basalt
Extrusive Igneous Rock (Mafic)
Hardness: 6 on the Mohs scale. Color: Dark gray to black, sometimes weathering to brownish. Luster: Dull to sub-earthy. Crystal structure: Aphanitic (fine-grained), often vesicular with gas cavities (vesicles). Specific gravity: 2.8 - 3.0.
- Hardness
- 6 on the Mohs scale
- Color
- Dark gray to black, sometimes weathering to brownish
- Luster
- Dull to sub-earthy
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Physical properties
Hardness: 6 on the Mohs scale. Color: Dark gray to black, sometimes weathering to brownish. Luster: Dull to sub-earthy. Crystal structure: Aphanitic (fine-grained), often vesicular with gas cavities (vesicles). Specific gravity: 2.8 - 3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity, iron- and magnesium-rich lava flows exposed at or very near the surface of a planet or moon. Can range in geological age from recent volcanic activity to billions of years old.
Uses & applications
Used widely in construction (crushed stone for road base, concrete aggregate), railroad ballast, and in the production of stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust, making up most of the ocean floor and large volcanic provinces like the Deccan Traps. Similar rocks also make up the dark maria regions on the Moon.
Field identification & locations
Easily identified by its dark color, fine-grained texture, and frequent vesicular (pitted) appearance from trapped gas bubbles. Found globally in volcanic regions, island arcs, and rift zones.
