igneous

Basalt River Stone

Extrusive Mafic Igneous Rock (primarily Plagioclase Feldspar and Pyroxene)

Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific Gravity: 2.8-3.0.

Hardness: 6-7 on Mohs scale
Color: Dark grey to black
Luster: Dull/Matte

Identified March 4, 2026More igneous →

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Physical properties

Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull/Matte; 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 has been Rounded by fluvial (river) or lacustrine (lake) erosion over hundreds to thousands of years.

Uses & applications

Used extensively in construction as aggregate, for road base, and railroad ballast. Smooth river stones are popular in landscaping, aquarium decor, and massage therapy (hot stones).

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 on the Moon, Mars, and Venus.

Field identification & locations

Identify in the field by its heavy weight (high density), dark color, and fine-grained texture that lacks visible crystals. Commonly found in volcanic regions or riverbeds downstream from volcanic highlands.

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