igneous

Basalt

Basalt (Mafic volcanic rock)

Hardness: 6.0 on Mohs scale; Color: dark grey to black; Luster: dull to sub-metallic; Structure: Fine-grained/aphanitic; Specific gravity: 2.8 - 3.0

Hardness: 6
Color: dark grey to black
Luster: dull to sub-metallic

Identified March 8, 2026More igneous →

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Physical properties

Hardness: 6.0 on Mohs scale; Color: dark grey to black; Luster: dull to sub-metallic; Structure: Fine-grained/aphanitic; Specific gravity: 2.8 - 3.0

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 moon. Occurs frequently in oceanic plates and volcanic hotspots.

Uses & applications

Used primarily in construction for aggregate, road base, concrete, and railroad ballast. Frequently used in industrial stone wool insulation and occasionally for decorative stone masonry.

Geological facts

Basalt is the most common rock type in Earth's crust and makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus, making it a key rock for understanding planetary formation.

Field identification & locations

Identify in the field by its dark color, fine-grained texture (crystals not visible to the naked eye), and high density. Commonly found in lava flow regions like the Pacific Northwest or ocean island chains.

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