igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None (conchoidal fracture); Specific Gravity: 2.8–3.0.
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
Identified More igneous →
Explore Basalt in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None (conchoidal fracture); 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 hot spot volcanoes. Ages vary from Precambrian to modern-day eruptions.
Uses & applications
Extensively used in construction for road base, concrete aggregate, railroad ballast, and dimension stone for pavers or countertops. High-quality scoria or vesicular basalt is used for landscaping.
Geological facts
Basalt is the most common rock type in Earth's crust and also covers large portions of the surfaces of the Moon, Mars, and Venus. On Earth, giant 'flood basalt' events have created massive formations like the Deccan Traps.
Field identification & locations
Identify in the field by its high density, dark color, and fine-grained texture (often showing small holes called vesicles). Found worldwide in volcanic regions such as Iceland, Hawaii, and the Pacific Northwest. For collectors, look for basalt containing olivine crystals.
