igneous

Basalt (Vesicular)

Basalt (Extrusive Igneous)

Hardness: 5-6 (Mohs); Color: dark grey to black or reddish-brown; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic) with vesicles; Density: 2.8–3.0 g/cm3

Hardness: 5-6 (Mohs)
Color: dark grey to black or reddish-brown
Luster: dull to sub-metallic

Identified May 25, 2026More igneous →

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Physical properties

Hardness: 5-6 (Mohs); Color: dark grey to black or reddish-brown; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic) with vesicles; Density: 2.8–3.0 g/cm3

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 moon. Many basalt specimens are millions of years old, originating from volcanic activity.

Uses & applications

Used extensively in construction for aggregate, road base, and railroad ballast. Polished basalt is used for tiles, monuments, and as 'hot stones' for massage therapy.

Geological facts

Basalt is the most common rock on Earth's surface and makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus. The holes (vesicles) were formed by gas bubbles escaping as the lava cooled.

Field identification & locations

Identify by its dark color, heavy weight (relative to size), and fine-grained texture. To distinguish from obsidian, look for a more dull luster and lack of conchoidal glass-like fracturing. Commonly found in volcanic regions like Hawaii, Iceland, and the Pacific Northwest.

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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