Basalt

Physical Properties

Hardness: 6.0; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained/microscopic); Cleavage: None; Specific gravity: 2.8-3.0.

Formation & Geological History

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Found in oceanic crust and volcanic regions worldwide across all geological eras.

Uses & Applications

Extensively used in construction as crushed stone for road bases, railroad ballast, and concrete aggregate. High-quality dense specimens are used as pavement slabs and in industrial casting.

Geological Facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floors. It is also found on the Moon and Mars.

Field Identification & Locations

Identify by its heavy weight (density), dark color, and lack of visible crystals. It common in volcanic fields, road cuts, and coastal areas near tectonic boundaries.

Identified on: 4/21/2026

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