Basalt

Physical Properties

Hardness: 6.0 on Mohs scale; Color: Dark grey to black; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0. Dense and heavy for its size.

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. Often found in oceanic crust and huge volcanic plateaus.

Uses & Applications

Extensively used in construction for road base, concrete aggregate, railroad ballast, and floor tiles. It is also used as 'lava rocks' for grill surfaces and landscaping.

Geological Facts

Basalt is the most common rock type in Earth's crust and makes up most of the ocean floors. It is also found on the Moon, Mars, and Venus.

Field Identification & Locations

Identify in the field by its dark color, fine grain (individual crystals are usually too small to see with the naked eye), and weight. Often forms hexagonal columns (columnar jointing) in large flows.

Identified on: 4/20/2026

Mode: Standard