igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 5-6 Mohs. Color: dark gray to black, often weathering to green or brown. Luster: dull to sub-metallic. Crystal structure: fine-grained (aphanitic) or porphyritic. Specific gravity: 2.8 - 3.0.
- Hardness
- 5-6 Mohs
- Color
- dark gray to black, often weathering to green or brown
- Luster
- dull to sub-metallic
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Physical properties
Hardness: 5-6 Mohs. Color: dark gray to black, often weathering to green or brown. Luster: dull to sub-metallic. Crystal structure: fine-grained (aphanitic) or porphyritic. 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. It represents the most common volcanic rock on Earth's crust.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. It is also used as dimension stone for flagstones and statues.
Geological facts
Basalt underlies more of Earth's surface than any other rock type. Most areas within Earth's ocean basins are underlain by basalt. It also makes up the lunar maria on the Moon.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and lack of visible crystals to the naked eye. Commonly found in volcanic regions, oceanic islands (like Hawaii), and mid-ocean ridges.
