igneous
Basalt
Aphanitic Mafic Igneous Rock
Hardness: 6 (Mohs scale); Color: dark gray to black; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic) or porphyritic; Specific gravity: 2.8–3.0. This specimen shows a vesicular texture with small holes.
- Hardness
- 6 (Mohs scale)
- Color
- dark gray to black
- Luster
- dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: dark gray to black; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic) or porphyritic; Specific gravity: 2.8–3.0. This specimen shows a vesicular texture with small holes.
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 is the most common rock type in the Earth's crust.
Uses & applications
Used extensively in construction for aggregate, road base, concrete, and railroad ballast. It is also used for cobblestones, statuary, and as an industrial mineral for cast basalt liners.
Geological facts
Basalt is not only found on Earth but is also the primary rock of the Moon's maria and covers large regions of Mars and Venus. It represents over 90% of all volcanic rock on Earth.
Field identification & locations
Identified in the field by its dark color, high density, and fine-grained texture. Commonly found in volcanic areas like Hawaii, Iceland, and the Deccan Traps. Collectors look for vesicles often filled with secondary minerals like zeolites.
