igneous

Basalt

Extrusive mafic igneous rock

Hardness: 6.0; Color: Dark grey, black, or dark brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0.

Hardness: 6
Color: Dark grey, black, or dark brown
Luster: Dull to sub-metallic

Identified April 5, 2026More igneous →

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Physical properties

Hardness: 6.0; Color: Dark grey, black, or dark brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0.

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Common in oceanic crust and volcanic regions.

Uses & applications

Used widely in construction as aggregate for roads and railroads, in concrete, and as high-quality building stone or paving sets.

Geological facts

Basalt is the most common rock type in the Earth's crust, making up almost all of the ocean floor. It is also found on the Moon and Mars.

Field identification & locations

Identify in the field by its heavy weight (high density), dark color, and lack of visible large crystal grains. Look for it in volcanic plateaus or near 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