Basalt

Physical Properties

Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull or 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

Used primarily in construction (crushed stone for road base and concrete aggregate), floor tiles, and as a raw material for stone wool insulation.

Geological Facts

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

Field Identification & Locations

Identify in the field by its dark color, heavy weight (density), and lack of visible crystals to the naked eye. Often found in volcanic regions or as rounded river cobbles like the specimen shown.

Identified on: 4/23/2026

Mode: Standard