igneous

Basalt

Hardness: 6.0; Color: Dark gray to black; Luster: Dull to earthy; Crystal structure: Aphanitic (fine-grained), often containing plagioclase feldspar and pyroxene; Specific gravity: 2.8-3.0.

Hardness: 6
Color: Dark gray to black
Luster: Dull to earthy

Identified April 4, 2026More igneous →

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Physical properties

Hardness: 6.0; Color: Dark gray to black; Luster: Dull to earthy; Crystal structure: Aphanitic (fine-grained), often containing plagioclase feldspar and pyroxene; 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 a moon. Most common rock in Earth's crust.

Uses & applications

Extensively used in construction, especially as road base, railroad ballast, and aggregate in concrete. Also used for high-quality floor tiles and landscape stone.

Geological facts

Basalt is the most common volcanic rock on Earth and also makes up most of the surface of the Moon, Mars, and Venus. The famous Giant's Causeway in Northern Ireland consists of columnar basalt.

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often shows a conchoidal or irregular fracture. Commonly found in lava flows and oceanic crust.

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