igneous

Basalt

Aphanitic Mafic Igneous Rock

Hardness: 6 (Mohs scale); Color: dark gray to black; Luster: dull to sub-glassy; Structure: fine-grained (aphanitic) or porphyritic; Cleavage: none; Specific Gravity: 2.8-3.0

Hardness: 6 (Mohs scale)
Color: dark gray to black
Luster: dull to sub-glassy

Identified January 12, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: dark gray to black; Luster: dull to sub-glassy; Structure: fine-grained (aphanitic) or porphyritic; Cleavage: none; Specific Gravity: 2.8-3.0

Formation & geological history

Formed from the rapid cooling of low-viscosity magnesium-rich and iron-rich lava (basaltic magma) at or very near the Earth's surface. Found in oceanic crust and volcanic regions.

Uses & applications

Extensively used in construction as crushed stone for road base, railroad ballast, and concrete aggregate. Also used for high-quality floor tiles and as a raw material for stone wool insulation.

Geological facts

Basalt is the most common rock type in the Earth's crust and covers most of the ocean floor. It is also found on the Moon, Mars, and Venus, making it a key component of the solar system's inner planets.

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and lack of visible crystals without a hand lens. Commonly found in lava flows, oceanic islands like Hawaii, and giant flood basalt plateaus.

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