Basalt

Physical Properties

Hardness: 6.0; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained), often containing plagioclase feldspar and pyroxene; Specific gravity: 2.8 to 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. Most basalt flows are from the Cenozoic era.

Uses & Applications

Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Sometimes used as dimensional stone for flooring 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 in the form of 'lunar maria'.

Field Identification & Locations

Identify by its dark color, heavy weight (density), and very fine-grained texture. It is commonly found in volcanic regions, oceanic islands, and mid-ocean ridges.

Identified on: 4/26/2026

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