igneous

Basalt

Extrusive Mafic Igneous Rock

Hardness: 6 (Mohs scale); Color: Dark gray to black, often weathering to brown; Luster: Dull to sub-vitreous; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8–3.0

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

Identified May 6, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark gray to black, often weathering to brown; Luster: Dull to sub-vitreous; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8–3.0

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. Common in oceanic crust and shield volcanoes.

Uses & applications

Used extensively in construction as road base, railroad ballast, concrete aggregate, and as a decorative landscaping stone. Also used in the manufacturing of stone wool insulation.

Geological facts

Basalt is the most common rock type in Earth's crust and covers most of the ocean floor. It is also common on the Moon and Mars, where it forms the dark 'maria'.

Field identification & locations

Identify by its dark color, heavy weight (density), and fine-grained texture. It often shows vesiculation (small holes) or columnar jointing. Found globally in volcanic regions like Hawaii, the Pacific Northwest (USA), and Iceland.

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