igneous

Basalt

Extrusive volcanic basalt

Hardness: 6 (Mohs); Color: Dark gray to black, often weathering to brown; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.8-3.0.

Hardness: 6 (Mohs)
Color: Dark gray to black, often weathering to brown
Luster: Dull/Earthy

Identified May 26, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs); Color: Dark gray to black, often weathering to brown; Luster: Dull/Earthy; 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 at the surface of a planet or moon; most of the Earth's oceanic crust is composed of basalt.

Uses & applications

Used primarily in construction for crushed stone, aggregate in concrete and asphalt, and occasionally for high-durability floor tiles or monuments.

Geological facts

Basalt is the most common rock type in the Earth's crust and also makes up the lunar maria on the Moon. It frequently forms distinctive columnar joints when cooling.

Field identification & locations

Identify by its heavy weight (high density), dark color, and very fine grains that are difficult to see with the naked eye. Commonly found in volcanic regions and along oceanic ridges.

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