igneous

Basalt

Extrusive mafic igneous rock

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

Hardness: 6 (Mohs scale)
Color: Dark grey to black
Luster: Dull/earthy

Identified May 25, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/earthy; 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. It can range in age from modern volcanic eruptions to billions of years old.

Uses & applications

Used primarily in construction (crushed stone for road base and concrete aggregate), high-tensile basalt fiber, and occasionally as structural building blocks.

Geological facts

Basalt is the most common rock type in the Earth's crust, making up most of the ocean floor and much of the surfaces of Mars and the Moon (lunar maria).

Field identification & locations

Identify by its dark color, heavy weight (relative to size), and fine-grained texture lacking visible crystals. Commonly found in volcanic regions, oceanic crust, and plate tectonic boundaries.

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