igneous

Basalt

Basalt (composition of plagioclase, pyroxene, and olivine)

Hardness: 6 on Mohs scale; Color: Black, dark grey, or charcoal; Luster: Submetallic to dull; Crystal structure: Aphanitic (fine-grained); Cleavage: Poor or absent; Specific gravity: 2.8–3.0

Hardness: 6 on Mohs scale
Color: Black, dark grey, or charcoal
Luster: Submetallic to dull

Identified June 3, 2026More igneous →

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Physical properties

Hardness: 6 on Mohs scale; Color: Black, dark grey, or charcoal; Luster: Submetallic to dull; Crystal structure: Aphanitic (fine-grained); Cleavage: Poor or absent; Specific gravity: 2.8–3.0

Formation & geological history

Formed from the rapid cooling of low-viscosity basaltic lava at or very near the Earth's surface. Basalts are found across all geological ages, from Precambrian to modern oceanic crust.

Uses & applications

Commonly used in construction as aggregate, for paving, and as 'hot stones' in massage therapy due to their heat retention qualities. Also used as decorative landscaping stones.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. Large-scale cooling of basalt can form unique hexagonal columns, such as at the Giant's Causeway.

Field identification & locations

Identify in the field by its dark color, heavy weight (relative to size), and fine-grained texture. Commonly found on beaches, riverbeds, and in volcanic areas. Tumbled versions like this are smooth and rounded.

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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Magnetite

Iron(II,III) oxide (Fe3O4)

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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