Basalt

Physical Properties

Hardness: 6.0; Color: dark grey to black or olive green; Luster: dull to earthy; Crystal structure: fine-grained (aphanitic) or porphyritic; Specific gravity: approx. 3.0

Formation & Geological History

Formed from the rapid cooling of magnesium-rich and iron-rich lava (mafic) at or very near the Earth's surface. Common in oceanic crust and volcanic islands.

Uses & Applications

Extensively used in construction, specifically as road base, concrete aggregate, railroad ballast, and for floor tiles.

Geological Facts

Basalt covers most of the ocean floor and is the most common volcanic rock in the solar system, also found in abundance on the Moon and Mars.

Field Identification & Locations

Identify by its heavy weight (density), dark color, and fine-grained texture. Commonly found near volcanic sites or in riverbeds as water-worn pebbles.

Identified on: 4/24/2026

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