Basalt (Beach Pebble)

Physical Properties

Hardness: 5-6 (Mohs); Color: Dark grey to charcoal black; Luster: Dull/Matte (earthy); Crystal structure: Fine-grained/Aphanitic; 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. This specific specimen has been shaped and smoothed into a 'Mexican Beach Pebble' or river stone through long-term water erosion.

Uses & Applications

Commonly used in landscaping, decorative stone for gardens, massage therapy (hot stones), and as a basic construction aggregate.

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 (for its size), dark uniform color, and fine-grained texture. It often shows light scuff marks when scratched against harder surfaces. This specific rounded shape indicates a history in a high-energy water environment like a beach or riverbed.

Identified on: 4/19/2026

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