Basalt

Physical Properties

Hardness: 6.0; Color: Dark grey to black, sometimes greenish when weathered; 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 a moon. It represents more than 90% of all volcanic rock on Earth.

Uses & Applications

Used primarily in construction for aggregate, road base, railroad ballast, and high-quality concrete. Finely ground basalt is also used as a soil amendment and in stone wool insulation.

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 extremely common on the Moon and Mars.

Field Identification & Locations

Identify in the field by its dark color, heavy weight (relative to size), and fine-grained texture which lacks visible crystals to the naked eye. It can often be found in volcanic regions or ancient lava flow beds.

Identified on: 4/26/2026

Mode: Standard