igneous

Basalt

Basalt (Mafic volcanic rock)

Hardness: 6; Color: Dark grey to black; Luster: Dull or earthy; Crystal structure: Aphanitic (fine-grained), often containing phenocrysts; Specific Gravity: 2.9-3.1

Hardness: 6
Color: Dark grey to black
Luster: Dull or earthy

Identified May 12, 2026More igneous →

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Physical properties

Hardness: 6; Color: Dark grey to black; Luster: Dull or earthy; Crystal structure: Aphanitic (fine-grained), often containing phenocrysts; Specific Gravity: 2.9-3.1

Formation & geological history

Extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron at or very near the Earth's surface. Found in oceanic crust and volcanic regions.

Uses & applications

Extensively used in construction for road base, concrete aggregate, railroad ballast, and high-quality asphalt. It is also used as a polishing stone and for stone carvings.

Geological facts

Basalt is the most common rock type on Earth's surface and also covers large areas of the Moon, Mars, and Venus. It forms the entirety of the oceanic crust.

Field identification & locations

Identify by its characteristic dark color, heavy weight (relative to size due to iron content), and lack of visible large crystal grains. Found in volcanic outcroppings and as river pebbles in volcanic regions.

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