igneous

Basalt

Basalt (Aphanitic Mafic Igneous)

Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained); Cleavage: None (conchoidal fracture); Specific Gravity: 2.8–3.0

Hardness: 6-7 Mohs
Color: Dark grey to black
Luster: Dull to sub-metallic

Identified May 28, 2026More igneous →

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Physical properties

Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained); Cleavage: None (conchoidal fracture); Specific Gravity: 2.8–3.0

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Most basalt found on Earth is from the Cenozoic era, though it has formed throughout geological history.

Uses & applications

Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. It is also used as dimension stone for tiles and in the manufacturing of rock 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, making it a key component of the terrestrial planets in our solar system.

Field identification & locations

Identify in the field by its dark color, heavy weight (relative to size), and very fine-grained texture where individual crystals are not visible to the naked eye. Often found in volcanic fields, oceanic islands, and mid-ocean ridges.

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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