igneous

Basalt River Stone

Basalt

Hardness: 6.0 on Mohs scale; Color: Black to dark gray; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.8 - 3.0.

Hardness: 6
Color: Black to dark gray
Luster: Dull to sub-metallic

Identified May 13, 2026More igneous →

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Physical properties

Hardness: 6.0 on Mohs scale; Color: Black to dark gray; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; 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 specimen has been rounded and smoothed by water erosion in a river or coastal environment.

Uses & applications

Commonly used in landscaping, construction (as aggregate), thermal massage (hot stones), and occasionally for carving or architecture.

Geological facts

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

Field identification & locations

Identify by its characteristic dark color, heavy weight for its size, and the absence of visible large crystals. Commonly found in volcanic regions or along riverbeds downstream from volcanic sources.

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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