Basalt (Water-worn Pebble)

Physical Properties

Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull to slightly waxy when wet, 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 at or near the Earth's surface. This specific specimen has been rounded and smoothed by mechanical weathering in a river or coastal environment.

Uses & Applications

Used primarily in construction (crushed stone), as a component in asphalt and concrete, or as ornamental river rocks in landscaping and decor.

Geological Facts

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

Field Identification & Locations

Identify by its dark color, high density (heavy for its size), and lack of visible crystals to the naked eye. In the field, look for it in volcanic regions, beaches, or riverbeds.

Identified on: 4/17/2026

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