igneous

Basalt River Pebble

Basalt (Mafic Extrusive Volcanic Rock)

Hardness: 5-6 Mohs. Color: Dark grey to black. Luster: Dull to sub-metallic. Crystal Structure: Aphanitic (fine-grained), often contains small vesicles or phenocrysts. Specific Gravity: 2.8-3.0.

Hardness: 5-6 Mohs
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified March 29, 2026More igneous →

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Physical properties

Hardness: 5-6 Mohs. Color: Dark grey to black. Luster: Dull to sub-metallic. Crystal Structure: Aphanitic (fine-grained), often contains small vesicles or phenocrysts. Specific Gravity: 2.8-3.0.

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 secondary-weathered and smoothed by fluvial (river) or glacial action, typically over thousands of years.

Uses & applications

Commonly used in construction as crushed stone or aggregate for concrete and asphalt. High-quality smooth basalt stones are popular in landscaping, aquarium decor, and hot stone massage therapy.

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. Large basaltic provinces can cover entire continents.

Field identification & locations

Identify in the field by its dark color, heavy weight (relative to size), and fine-grained texture. These smooth 'river stones' are commonly found in stream beds, volcanic coastal regions, and glacial deposits. Collectors value them for their tactile smoothness and aesthetic simplicity.

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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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)

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Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Blue Apatite

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

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Magnetite

Magnetite (Fe3O4)

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