igneous

Basalt

Mafic volcanic 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; Cleavage: None; Specific gravity: 2.8–3.0

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

Identified March 18, 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; 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. Most common in oceanic crust and volcanic hotspots.

Uses & applications

Extensively used in construction as aggregate for road base, railroad ballast, and concrete. Also used for high-quality floor tiles and stonework in landscaping.

Geological facts

Basalt is the most abundant bedrock on Earth, making up the vast majority of the ocean floor. It is cũng the primary rock type on the Moon's Maria and large portions of Mars and Venus.

Field identification & locations

Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often shows vesiculation (small air bubbles). Common in regions like the Pacific Northwest, Hawaii, and Iceland.

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