igneous

Basalt

Aphanitic Mafic Igneous Rock

Hardness: 6 (Mohs); Color: Dark gray to black; Luster: Dull to matte; Crystal structure: Aphanitic (fine-grained); Cleavage: None/Conchoidal; Specific gravity: 2.8 - 3.0

Hardness: 6 (Mohs)
Color: Dark gray to black
Luster: Dull to matte

Identified May 31, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs); Color: Dark gray to black; Luster: Dull to matte; Crystal structure: Aphanitic (fine-grained); Cleavage: None/Conchoidal; 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. It is the most common volcanic rock on Earth, covering much of the ocean floors.

Uses & applications

Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Also used for statues or as heat-retaining stones in spas.

Geological facts

Basalt is equivalent in composition to gabbro, but gabbro is intrusive (cooled slowly underground). Basalt is found on Mars, Venus, and the Moon (the dark lunar Maria are basaltic plains).

Field identification & locations

Identify by its weight, dark color, and fine-grained texture lacking visible crystals. It frequently forms columnar joints. Found globally in volcanic regions like Hawaii, Iceland, and the Deccan Traps.

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