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 surface of a terrestrial planet or moon. Most basalt flows on Earth occur mid-ocean at ridges.

Uses & Applications

Used primarily in construction (crushed stone, concrete aggregate, asphalt pavement), railroad ballast, and sometimes in industrial casting and stone wool insulation.

Geological Facts

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

Field Identification & Locations

Identify by its dark color, heavy weight (relative to size), and fine-grained texture. It often weathers to a reddish-brown color due to iron oxidation. Commonly found in volcanic regions and riverbeds near igneous outcrops.

Identified on: 4/14/2026

Mode: Standard