igneous

Basalt

Basalt (Mafic volcanic rock)

Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.9–3.1

Hardness: 6 on Mohs scale
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified May 26, 2026More igneous →

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Physical properties

Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.9–3.1

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 basalt on Earth was formed by decompression melting of the mantle.

Uses & applications

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

Geological facts

Basalt is the most common rock type in the Earth's crust, making up most of the ocean floor. Large parts of the Moon's surface, the lunar maria, are also composed of basalt.

Field identification & locations

Identify by its dark color, heavy weight (relative to size), and fine-grained texture. It often shows a 'peppered' appearance from small crystals and is commonly found in volcanic regions and ocean basins.

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