igneous

Basalt with Plagioclase Phenocrysts

Porphyritic Basalt

Hardness: 6-7 on Mohs scale. Color: Dark grey to black matrix with white or light-colored inclusions. Luster: Dull to sub-vitreous. Crystal structure: Aphanitic (fine-grained) matrix with visible macro-crystals (phenocrysts).

Hardness: 6-7 on Mohs scale
Luster: Dull to sub-vitreous

Identified April 12, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The larger white crystals formed earlier within the cooling magma chamber before the final eruption.

Uses & applications

Used primarily in construction as aggregate for concrete and asphalt, road base, and railroad ballast. Exceptionally durable varieties are used for floor tiles and monuments.

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 in abundance on the Moon and Mars.

Field identification & locations

Identified by its dark, heavy, and fine-grained 'stony' matrix often containing distinct pinpoint or tabular lath-shaped white crystals. Common in volcanic regions and coastal areas near tectonic boundaries.

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