igneous

Basalt (River Stone/Pebble)

Basalt (Extrusive Igneous Rock)

Hardness: 6-7 (Mohs scale); Color: Dark grey to black, weathering to brown/green; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained) to porphyritic with small visible phenocrysts; Cleavage: None/Irregular; Specific gravity: 2.8–3.0.

Hardness: 6-7 (Mohs scale)
Color: Dark grey to black, weathering to brown/green
Luster: Dull/Matte

Identified March 21, 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 specimen has been rounded by fluvial (river) or coastal erosion processes. Geological age varies by locality but occurs throughout Earth's history.

Uses & applications

Used widely in construction as crushed stone (aggregate) for roads and railways. Smooth river versions are popular for decorative landscaping, 'hot stone' massage therapy, and aquarium decor.

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 and Mars. When cooled in large masses, it can form striking hexagonal columns like the Giant's Causeway.

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It will not react with acid (unlike limestone). Commonly found in volcanic regions, riverbeds, and beaches.

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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)

mineral