igneous

Basalt

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

Hardness: 6 (Mohs)
Color: Dark gray to black
Luster: Dull to sub-metallic

Identified May 12, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs); Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; 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. Most basalt in this smooth form originates from volcanic activity and is later weathered by water.

Uses & applications

Used primarily in construction (crushed stone, concrete aggregate, asphalt pavement), decorative landscaping, and occasionally for stonework or 'hot stone' massage therapy due to heat retention.

Geological facts

Basalt is the most common rock on Earth's surface and also covers massive areas of the Moon's surface (the lunar maria). It is the primary rock type of the ocean floor.

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and lack of visible crystals. Commonly found in volcanic regions or as rounded cobbles in riverbeds and coastal areas.

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