igneous

Basalt

Mafic igneous rock (primarily Plagioclase feldspar and Pyroxene)

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.9–3.1

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

Identified April 10, 2026More igneous →

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Physical properties

Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific gravity: 2.9–3.1

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

Used extensively in construction as aggregate for concrete and asphalt, road base, railroad ballast, and sometimes as a dimension stone for floor tiles or monuments.

Geological facts

Basalt is the most common rock on Earth and also makes up much of the surfaces of the Moon, Mars, and Venus. The Giant's Causeway in Ireland is a famous example of columnar basalt joints.

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and lack of visible crystals to the naked eye. Found in volcanic regions and volcanic plateaus globally.

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