igneous

Basalt

Extrusive mafic igneous rock

Hardness: 6.0; Color: Dark grey to black; Luster: Dull/earthy; Structure: Fine-grained/aphanitic; Specific gravity: 2.8 - 3.0

Hardness: 6
Color: Dark grey to black
Luster: Dull/earthy

Identified April 9, 2026More igneous →

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Physical properties

Hardness: 6.0; Color: Dark grey to black; Luster: Dull/earthy; Structure: Fine-grained/aphanitic; 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.

Uses & applications

Used primarily in construction (crushed stone for road base, concrete aggregate, railroad ballast), and as a raw material for stone wool insulation.

Geological facts

Basalt is the most common rock on Earth's surface, making up most of the ocean floor and much of the surfaces of the Moon, Mars, and Venus.

Field identification & locations

Identify by its dark color, fine-grained texture (crystals are too small to see with the naked eye), and high density. Commonly found in volcanic fields and oceanic crust areas.

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