Basalt (Weathered)

Physical Properties

Hardness: 6 (Mohs); Color: Dark grey to reddish-brown (weathered); Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8–3.0

Formation & Geological History

Formed from the rapid cooling of low-viscosity basaltic lava at or very near the Earth's surface. This specific piece shows rounding from alluvial or glacial transport and iron oxidation (rusting) on the surface.

Uses & Applications

Primarily used as aggregate in construction, road base, and railroad ballast. Larger pieces are used in pavers or as dimension stone.

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 in the field by its dark interior color, heavy weight (relative to size), and fine-grained texture. It often weathers into a reddish-tan crust due to high iron content.

Identified on: 5/15/2026

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