igneous

Basalt River Stone

Basalt (Mafic volcanic rock)

Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0. This specimen is water-worn and smooth.

Hardness: 6-7 Mohs
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified May 19, 2026More igneous →

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Physical properties

Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0. This specimen is water-worn and smooth.

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 rounded and polished by hydraulic action in a river or coastal environment.

Uses & applications

Utilized in construction as aggregate, for paving, in 'hot stone' massage therapy, as aquarium decor, and in 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 by its high density, dark color, and lack of visible crystals to the naked eye. River-worn specimens are found in any drainage basin cutting through volcanic terrain.

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mineral

Dark Igneous Rock (Likely Basalt or Diabase)

Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.

Igneous