igneous

Basalt

Basalt (Mafic volcanic rock)

Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Density: 2.8-3.0 g/cm³; Cleavage: None/Irregular fracture.

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

Identified April 6, 2026More igneous →

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Physical properties

Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Density: 2.8-3.0 g/cm³; Cleavage: None/Irregular fracture.

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 in Earth's crust, primarily forming the ocean floor.

Uses & applications

Extensively used in construction for aggregate, road base, railroad ballast, and concrete. It is also used as a material for stonewalling and in the production of basalt fiber for high-tensile strength applications.

Geological facts

Basalt makes up more than 90% of all volcanic rock on Earth. It is also found in abundance on the Moon (the dark 'Maria' plains) and Mars. It can form unique hexagonal columns during cooling, known as columnar jointing.

Field identification & locations

Identify in the field by its dark color, fine-grained texture (crystals not visible to the naked eye), and high density. Commonly found at volcanic sites, tectonic plate boundaries, and oceanic island chains like Hawaii.

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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