igneous

Basalt

Mafic Volcanic Rock (composed of plagioclase, pyroxene, and olivine)

Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8–3.0

Hardness: 6 (Mohs scale)
Color: Dark gray to black
Luster: Dull to sub-vitreous

Identified February 17, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8–3.0

Formation & geological history

Formed from the rapid cooling of low-viscosity magnesium-rich and iron-rich lava at or very near the Earth's surface. This specimen appears to be a water-worn or weathered pebble likely from the Cenozoic era or older depending on the local bedrock.

Uses & applications

Extensively used in construction as aggregate (crushed stone), for paving and road base, and occasionally in sculptures or as a heat-retaining stone in 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.

Field identification & locations

Identify by its dark color, heavy weight for its size, and lack of visible crystals. It is commonly found near volcanic sites or in riverbeds where it has been transported from volcanic highlands. Collectors should look for vesicles (gas bubbles) or mineral inclusions.

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

Blue Apatite

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

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral