igneous

Vesicular Basalt

Extrusive mafic igneous rock

Hardness: 5-6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) with vesicles; Specific gravity: 2.8-3.0

Hardness: 5-6 (Mohs scale)
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified May 28, 2026More igneous →

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Physical properties

Hardness: 5-6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) with vesicles; 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 Earth's surface. The small holes (vesicles) are created by gas bubbles escaping from the lava as it solidifies.

Uses & applications

Used in construction as road base, concrete aggregate, and railroad ballast. Larger pieces are popular for aquarium landscaping and garden decoration.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon and Mars.

Field identification & locations

Identify by its dark color, heavy weight compared to other light-colored rocks of the same size, and the presence of small pits or holes on the surface. Commonly found in volcanic regions.

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