igneous

Vesicular Basalt

Extrusive mafic igneous rock

Hardness: 5-6 (Mohs); Color: Dark grey to black; Luster: Dull or earthy; Structure: Aphanitic with vesicles; Cleavage: None; Specific Gravity: 2.8–3.0

Hardness: 5-6 (Mohs)
Color: Dark grey to black
Luster: Dull or earthy

Identified May 9, 2026More igneous →

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Physical properties

Hardness: 5-6 (Mohs); Color: Dark grey to black; Luster: Dull or earthy; Structure: Aphanitic with vesicles; Cleavage: None; Specific Gravity: 2.8–3.0

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. The 'vesicles' (holes) are caused by gas bubbles trapped in the cooling lava. Found in volcanic regions worldwide.

Uses & applications

Used primarily in construction for road base, concrete aggregate, and railroad ballast. Highly vesicular specimens are used in landscaping and as 'lava rocks' for grills.

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 in the field by its dark color, heavy weight (relative to size), and characteristic holes or pits on the surface. Commonly found in old volcanic flows and near mountain ranges.

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