Basalt

Physical Properties

Hardness: 6.0; Color: Dark gray to black (weathered to dull purplish-brown); Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0; Cleavage: None.

Formation & Geological History

Formed from the rapid cooling of low-viscosity magnesium-rich and iron-rich lava. This specimen appears water-worn, likely from a coastal or riverine environment where volcanic activity occurred during the Cenozoic era.

Uses & Applications

Used extensively in construction as road base, concrete aggregate, and railroad ballast. Dense varieties are used for high-quality floor tiles and monuments.

Geological Facts

Basalt is the most common rock type in the Earth's crust and covers most of the ocean floor. It is juga common on the Moon and Mars.

Field Identification & Locations

Identify by its dark color, heavy weight (relative to size), and fine-grained texture with no visible crystals to the naked eye. Commonly found on beaches near volcanic regions.

Identified on: 5/3/2026

Mode: Standard