igneous

Basalt

Hardness: 6.0 on Mohs scale; Color: Black, dark gray, or dark brown; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8–3.0.

Hardness: 6
Color: Black, dark gray, or dark brown
Luster: Dull to sub-metallic

Identified April 8, 2026More igneous →

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Physical properties

Hardness: 6.0 on Mohs scale; Color: Black, dark gray, or dark brown; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; 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 basalt on Earth was formed during the Cenozoic era, though it can date back billions of years.

Uses & applications

Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. It is also used as dimension stone for tiles and floorings, and occasionally in stone sculpture.

Geological facts

Basalt is the most common rock type in the Earth's crust, making up most of the ocean floor. It is also common on the Moon, Mars, and Venus. The Giant's Causeway in Northern Ireland is a famous example of columnar basalt.

Field identification & locations

Identify by its dark color, heavy weight (density), and fine-grained texture. It often shows small pits (vesicles) from gas bubbles. Found globally in volcanic regions and ocean basins.

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