igneous

Basalt

Basalt (Aphanitic Mafic Igneous Rock)

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic), sometimes vesicular; Cleavage: None (conchoidal fracture); Specific Gravity: 2.8–3.0.

Hardness: 6 (Mohs scale)
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified March 23, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. While basaltic volcanism has occurred throughout Earth's history, most seafloor basalt is less than 200 million years old.

Uses & applications

Extensively used in construction as crushed stone for road base, concrete aggregate, and railroad ballast. It is also used in the manufacturing of rock wool insulation and as high-quality floor tiles.

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 moon and Mars; the dark 'seas' (maria) on the Moon are actually giant basaltic plains.

Field identification & locations

Identify in the field by its dark color, heavy weight (relative to size), and lack of visible crystals to the naked eye. It is commonly found in volcanic regions, oceanic crust, and large igneous provinces like the Deccan Traps or Columbia River Plateau.

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