igneous
Basalt (Micromount)
Extrusive Mafic Igneous Rock
Hardness: 6 (Mohs scale); Color: Black to dark gray; Luster: Dull to sub-metallic (if olivine is present); Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Black to dark gray
- Luster
- Dull to sub-metallic (if olivine is present)
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs scale); Color: Black to dark gray; Luster: Dull to sub-metallic (if olivine is present); 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 exposed at or very near the surface of a terrestrial planet or moon. Most terrestrial basalt formed during the Cenozoic era, though it can date back billions of years.
Uses & applications
Used primarily in construction (aggregate, road base, railroad ballast) and for manufacturing stone wool insulation. Small specimens are used in educational kits.
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 (density), and lack of visible large crystals. Commonly found in volcanic fields, oceanic ridges, and plateau provinces like the Deccan Traps or Columbia River Plateau.
