Basalt (Weathered River Stone)

Physical Properties

Hardness: 6-7 on Mohs scale; Color: Dark grey to charcoal when dry, black when wet; Luster: Dull or earthy (weathered); 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 or very near the Earth's surface. This specific specimen shows signs of fluvial erosion (smoothing by water) and is likely from the Cenozoic or Mesozoic era depending on the local geology.

Uses & Applications

Commonly used as crushed stone for road base, concrete aggregate, railroad ballast, and high-quality asphalt. It is also used in 'hot stone' massage and as river rock for landscaping.

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 in the field by its heavy weight (density), dark color, and lack of visible crystals to the naked eye. Often found in volcanic regions or transported by rivers as smooth pebbles.

Identified on: 4/17/2026

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