igneous

Basalt

Basalt (Aphanitic Mafic Igneous Rock)

Hardness: 6 (Mohs scale); Color: Black to dark gray; Luster: Dull to sub-metallic; Crystal Structure: Very fine-grained (aphanitic) due to rapid cooling; Cleavage: None; Specific Gravity: 2.8 - 3.0 (dense).

Hardness: 6 (Mohs scale)
Color: Black to dark gray
Luster: Dull to sub-metallic

Identified March 22, 2026More igneous →

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Physical properties

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 is less than 200 million years old, specifically in oceanic crust.

Uses & applications

Primary use is as aggregate in construction projects (crushed stone for road base, concrete, and railroad ballast). Higher-quality specimens are used in stone masonry, floor tiles, and garden ornaments.

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 found on the Moon, Mars, and Venus in the form of 'Maria' or dark plains.

Field identification & locations

Identify by its dark color, heavy weight (density), and fine-grained texture. It often shows small holes (vesicles) where gas was trapped. Commonly found along oceanic ridges, volcanic islands (like Hawaii), and large continental flood basalt provinces.

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