igneous

Basalt

Basalt (Mafic volcanic rock)

Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.8-3.0.

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

Identified May 27, 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) to porphyritic; 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 basalt on Earth was formed during the Mesozoic and Cenozoic eras.

Uses & applications

Extensively used in construction for aggregate, road base, railroad ballast, and high-quality paving stones. It is also used as raw material for stone wool insulation.

Geological facts

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

Field identification & locations

Look for the characteristic dark, dense, fine-grained texture. It often breaks into angular fragments. Common in volcanic regions and oceanic islands like 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