igneous

Basalt

Aphanitic Mafic Igneous Rock

Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), Specific Gravity: 2.8–3.0.

Identified January 12, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), 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 moon. Most basalt on Earth is formed at mid-ocean ridges through seafloor spreading.

Uses & applications

Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Some varieties are used for architectural veneer or stone carvings.

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 common on the Moon, Mars, and Venus.

Field identification & locations

Identified by its dark color, heavy weight (relative to size), and very fine-grained texture. Commonly found in volcanic regions or as water-worn pebbles in riverbeds and beaches.

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