Basalt

Physical Properties

Hardness: 6.0; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; 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 Earth's surface. Can range from Recent to Precambrian in age.

Uses & Applications

Extensively used in construction for aggregate, road base, railroad ballast, and high-quality paving stones. It is also used as raw material for stone wool insulation.

Geological Facts

Basalt is the most common rock on Earth's surface, making up most of the ocean floor. It is also extremely common on the Moon, Mars, and Venus.

Field Identification & Locations

Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often shows vesicular (bubbly) textures or columnar jointing in large outcrops. Commonly found in volcanic regions and riverbeds near volcanic flows.

Identified on: 4/27/2026

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