igneous

Basalt

Basalt (Mafic Extrusive Igneous Rock)

Hardness: 6 on Mohs scale; Color: Dark grey to black or brownish-red; Luster: Dull to sub-metallic; Structure: Aphanitic (fine-grained) to vesicular; Cleavage: None (conchoidal fracture); Specific Gravity: 2.8–3.0

Hardness: 6 on Mohs scale
Color: Dark grey to black or brownish-red
Luster: Dull to sub-metallic

Identified January 12, 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. Common in oceanic crust and mid-ocean ridges. Its age can range from modern eruptions to hundreds of millions of years old.

Uses & applications

Used extensively in construction as crushed stone for road bases, concrete aggregate, and railroad ballast. It is also used in the manufacturing of rock wool insulation and as a dimension stone for flooring or monuments.

Geological facts

Basalt is the most common volcanic rock in the solar system, covering most of the ocean floors on Earth and forming the 'seas' (maria) on the Moon. This specific specimen appears to be worked into an anthropogenic tool shape, such as a projectile point or scraper.

Field identification & locations

Identify in the field by its dark color, fine-grained texture, and high density. Look for small holes (vesicles) or a 'scaly' conchoidal fracture where it has been chipped. Commonly found in volcanic regions such as the Pacific Northwest, Iceland, and Hawaii.

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