igneous
Basalt
Aphanitic Mafic Igneous Rock
Hardness: 5-6 Mohs; Color: dark grey to black or greenish-grey; Luster: dull to sub-metallic; Crystal Structure: fine-grained (aphanitic) or porphyritic; Cleavage: none; Specific Gravity: 2.8-3.0
- Hardness
- 5-6 Mohs
- Color
- dark grey to black or greenish-grey
- Luster
- dull to sub-metallic
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 5-6 Mohs; Color: dark grey to black or greenish-grey; Luster: dull to sub-metallic; Crystal Structure: fine-grained (aphanitic) or porphyritic; Cleavage: none; 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 specimens are less than 200 million years old due to tectonic recycling.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Also used for high-temperature stone wool insulation and occasionally carved into monuments.
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 common on the Moon, Mars, and Venus.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size), and fine-grained texture. It often shows columnar jointing or vesicular (pitted) surfaces if formed with gas bubbles.
