igneous

Basalt

Basalt (Mafic Extrusive Igneous Rock)

Hardness: 6 (Mohs scale), Color: Dark grey to black or greenish-black, Luster: Dull to sub-metallic, Structure: Fine-grained/aphanitic with some vesicles or phenocrysts, Cleavage: None

Identified May 25, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale), Color: Dark grey to black or greenish-black, Luster: Dull to sub-metallic, Structure: Fine-grained/aphanitic with some vesicles or phenocrysts, Cleavage: None

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. Occurs throughout geological time from Precambrian to present.

Uses & applications

Extensively used in construction for road base, concrete aggregate, railroad ballast, and dimension stone for buildings. Also used as stone wool for insulation.

Geological facts

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

Field identification & locations

Identify by its dark color, heavy weight (high specific gravity), and very fine-grained texture. Commonly found in volcanic fields, oceanic islands, and mid-ocean ridges.

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