igneous

Basalt

Extrusive mafic rock

Hardness: 6-7 on Mohs scale; Color: Dark grey to black, often weathering to brown/green; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None; Specific Gravity: 2.8-3.0.

Hardness: 6-7 on Mohs scale
Color: Dark grey to black, often weathering to brown/green
Luster: Dull to sub-metallic

Identified May 28, 2026More igneous →

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Physical properties

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. Most common rock in Earth's crust (oceanic).

Uses & applications

Extensively used in construction as aggregate for roads, railroad ballast, and concrete; also used as a dimension stone for floor tiles and monument sculptures.

Geological facts

Basalt is the most common rock type on the surface of the Moon and Mars. It provides the dark coloring of the lunar maria.

Field identification & locations

Identify by its heavy weight (high density), fine grain size where individual crystals are not visible to the naked eye, and dark color. Commonly found in volcanic regions, oceanic islands, and mid-ocean 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