igneous

Basalt

Basalt (Mafic Extrusive)

Hardness: 6.0 on Mohs scale; Color: dark grey to black (weathered to grey-green); Luster: dull to earthy; Structure: fine-grained (aphanitic), often contains small vesicles or phenocrysts; Specific Gravity: 2.8 - 3.0.

Hardness: 6
Color: dark grey to black (weathered to grey-green)
Luster: dull to earthy

Identified June 2, 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 surface of a terrestrial planet or ocean floor. This specimen likely underwent river or coastal erosion to achieve its smooth, rounded shape.

Uses & applications

Extensively used in construction as crushed stone, road base, concrete aggregate, railroad ballast, and for paving stones. Fine specimens are used in landscape design.

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.

Field identification & locations

Identify by its dark color, high density, and fine-grained texture. Commonly found in volcanic regions, riverbeds, and along shorelines. For collectors, look for smoothness and absence of large cracks.

Other igneous specimens

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Granite

Igneous

Granite

Igneous

Blue Apatite

Fluorapatite (Ca5(PO4)3F)

mineral

Dalmatian Jasper

Aplite with Arfvedsonite inclusions

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Magnetite

Iron(II,III) oxide (Fe3O4)

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