igneous

Basalt River Stone

Basalt (Mafic volcanic rock, primarily Plagioclase and Pyroxene)

Hardness: 6 (Mohs scale); Color: Dark grey to charcoal black with white mineral weathering or streaks; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0.

Hardness: 6 (Mohs scale)
Luster: Dull to sub-metallic

Identified March 14, 2026More igneous →

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Physical properties

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 further shaped by fluvial erosion (river action), smoothing its edges into a rounded 'cobble' or 'pebble.'

Uses & applications

Commonly used as high-density construction aggregate, in the production of rock wool insulation, for landscaping, and as 'hot stones' for massage therapy due to high heat retention.

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. When basalt cools slowly, it can form spectacular hexagonal columns like those at the Giant's Causeway.

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often shows 'desert varnish' or white surface oxidation when weathered. Found globally in volcanic regions and riverbeds downstream from volcanic sources.

Other igneous specimens

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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

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Magnetite

Magnetite (Fe3O4)

mineral