igneous

Basalt

Basalt (Mafic volcanic rock)

Hardness: 6-7 on Mohs scale. Color: Dark gray to black. Luster: Dull to sub-metallic. Crystal structure: Aphanitic (fine-grained), sometimes containing phenocrysts. Specific gravity: 2.8-3.0.

Hardness: 6-7 on Mohs scale
Color: Dark gray to black
Luster: Dull to sub-metallic

Identified April 6, 2026More igneous →

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Physical properties

Hardness: 6-7 on Mohs scale. Color: Dark gray to black. Luster: Dull to sub-metallic. Crystal structure: Aphanitic (fine-grained), sometimes containing phenocrysts. Specific gravity: 2.8-3.0.

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava (basaltic lava) at or near the Earth's surface. It is the most common volcanic rock on Earth and covers much of the ocean floor.

Uses & applications

Extensively used in construction for aggregate in concrete and asphalt, road base, railroad ballast, and sometimes as a dimension stone for flooring or monuments.

Geological facts

Basalt also composes much of the crust of the Moon, Mars, and Venus. On Earth, famous formations like the Giant's Causeway in Ireland consist of columnar basalt joints.

Field identification & locations

Identify in the field by its heavy weight for its size, dark color, and very fine grains that are often invisible to the naked eye. It commonly forms in volcanic regions and ocean ridges.

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