Basalt

Physical Properties

Hardness: 6 (Mohs scale); Color: Dark grey to black, weathering to brown/green; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 to 3.0

Formation & Geological History

Formed from the rapid cooling of low-viscosity magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. Most common rock in the Earth's crust.

Uses & Applications

Extensively used in construction for aggregate, asphalt, and concrete; also used in rock wool insulation and as a decorative stone in landscaping.

Geological Facts

Basalt is the most common volcanic rock on Earth. It also makes up most of the surface of the Moon (the dark lunar maria) and is the primary rock type on Mars and Venus.

Field Identification & Locations

Identify in the field by its very fine-grained texture, dark color, and high density. It often forms hexagonal pillars (columnar jointing) in large flows. Found globally in oceanic crust and volcanic hotspots like Hawaii or Iceland.

Identified on: 4/13/2026

Mode: Standard