Basalt (River Stone)

Physical Properties

Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull to earthy; Structure: Fine-grained (aphanitic) to glassy; Specific Gravity: 2.8–3.0. This specimen shows a rounded, water-worn texture.

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 piece has been secondary-processed by fluvial (river) erosion, rounding its sharp edges over time.

Uses & Applications

Used extensively in construction (aggregate), high-strength floor tiles, and as decorative stone in landscaping. Smooth river basalt is often used in massage therapy (hot stone massage).

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 extensively on the Moon and Mars.

Field Identification & Locations

Identify by its dark color, heavy weight for its size, and lack of visible large crystals. Commonly found in riverbeds or near volcanic regions. It will not react with acid unlike limestone.

Identified on: 4/14/2026

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