igneous

Basalt River Stone

Aphanitic Mafic Igneous Rock (primarily Plagioclase and Pyroxene)

Hardness: 5-6 (Mohs); Color: Dark grey to charcoal black; Luster: Dull to sub-vitreous; Structure: Fine-grained (aphanitic) with rounded water-worn texture; Cleavage: None/Irregular; Specific Gravity: 2.8-3.0

Hardness: 5-6 (Mohs)
Color: Dark grey to charcoal black
Luster: Dull to sub-vitreous

Identified March 4, 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 near the Earth's surface. This specific specimen has been significantly rounded and smoothed by fluvial (river) or coastal erosion processes.

Uses & applications

Commonly used in landscaping as decorative river rock, in construction as road base or concrete aggregate, and sometimes in hot stone massage 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 in abundance on the Moon and Mars.

Field identification & locations

Identify in the field by its heavy weight relative to size, dark uniform color, and lack of visible crystals. Commonly found in volcanic regions or in 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