igneous

Basalt

Basalt (containing mainly Plagioclase feldspar and Pyroxene)

Hardness: 6 on Mohs scale; Color: typically dark gray to black; Luster: dull to earthy; Crystal structure: fine-grained (aphanitic) due to rapid cooling; Cleavage: none; Specific gravity: 2.8 - 3.0.

Hardness: 6 on Mohs scale
Color: typically dark gray to black
Luster: dull to earthy

Identified March 15, 2026More igneous →

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Physical properties

Hardness: 6 on Mohs scale; Color: typically dark gray to black; Luster: dull to earthy; Crystal structure: fine-grained (aphanitic) due to rapid cooling; 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 be found in oceanic crust and volcanic hotspots across all geological ages.

Uses & applications

Extensively used in construction for aggregate in concrete and asphalt, road base, railroad ballast, and sometimes as a dimension stone for floor tiles or monument bases.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It also covers large areas of the Moon, Mars, and Venus, manifesting as 'maria' (dark plains) on the moon.

Field identification & locations

Identify by its dark color, heavy weight (relative to size), and fine-grained texture which lacks visible crystals to the naked eye. Commonly found in volcanic regions, near oceanic ridges, or as glacial erratics in some regions.

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

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Magnetite

Magnetite (Fe3O4)

mineral