igneous
Basalt
Basalt (Aphanitic Mafic Igneous Rock)
Hardness: 6 (Mohs scale); Color: Dark grey to black, sometimes weathering to brown or green; Luster: Dull to earthy; Crystal Structure: Fine-grained (aphanitic), micro-crystalline; Cleavage: None; Specific Gravity: 2.8 - 3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black, sometimes weathering to brown or green
- Luster
- Dull to earthy
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black, sometimes weathering to brown or green; Luster: Dull to earthy; Crystal Structure: Fine-grained (aphanitic), micro-crystalline; Cleavage: None; Specific Gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava (mafic) at or very near the Earth's surface. Found in oceanic crust, volcanic islands, and plateau basalt provinces.
Uses & applications
Primarily used in construction as aggregate (crushed stone), road base, railroad ballast, and in some architectural stone applications. Also used for making stone wool (insulation).
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found extensively on the Moon (the dark lunar maria) and Mars.
Field identification & locations
Identify by its dark color, heavy weight for its size, and the absence of large visible crystals. It often breaks into angular pieces or exhibits columnar jointing in large formations. Found globally in volcanic regions.
