igneous

Basalt

Mafic Igneous Rock

Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8 - 3.0

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

Identified May 29, 2026More igneous →

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Physical properties

Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; 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 a moon. Most common rock type in the Earth's crust (oceanic crust).

Uses & applications

Used primarily in construction for aggregate, road base, concrete, and railroad ballast. Also used as dimension stone and for industrial floor tiles.

Geological facts

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

Field identification & locations

Identify by its dark color, heavy weight (relative to size), and fine-grained texture. Found globally in volcanic regions such as Iceland, Hawaii, and the Deccan Traps. Collectors look for vesicles (gas bubbles) often filled with secondary minerals like zeolites.

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