Basalt (Beach Pebble)

Physical Properties

Hardness: 6 on Mohs scale; Color: Dark grey to dull black; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8 - 3.0

Formation & Geological History

Formed from the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. This specific specimen has been rounded and smoothed by water erosion in a high-energy environment like a river or beach.

Uses & Applications

Mainly used as crushed aggregate for construction, road base, and railroad ballast. Smooth pebbles are often used in decorative landscaping or as massage stones.

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 heavy weight (density), dark color, and lack of visible crystals. Commonly found in volcanic regions and on beaches near oceanic crust boundaries.

Identified on: 4/30/2026

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