Basalt

Physical Properties

Hardness: 6-7 (Mohs scale), Color: Dark grey to black, Luster: Dull to sub-metallic, 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. It can be of any age, from billions of years old to forming today in volcanic regions like Iceland.

Uses & Applications

Extensively used in construction for road base, concrete aggregate, railroad ballast, and as a dimension stone for floor tiles and monuments.

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 found on the Moon and Mars.

Field Identification & Locations

Identify by its dark color, heavy weight (density), and very fine-grained texture where individual crystals are not visible to the naked eye. Commonly found in volcanic fields, oceanic islands, and mid-ocean ridges.

Identified on: 4/18/2026

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