Basalt

Physical Properties

Hardness: 6.0 on Mohs scale; Color: dark grey to black; Luster: dull to earthy; Crystal structure: aphanitic (fine-grained); 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.

Uses & Applications

Commonly used as an aggregate in construction projects, road base, concrete, and as high-quality railroad ballast.

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 common on the Moon and Mars.

Field Identification & Locations

Identify in the field by its dark color, fine grain size, and heavy weight relative to its size. It often forms hexagonal pillars (columnar jointing) in large flows.

Identified on: 4/22/2026

Mode: Standard