Igneous

Porphyritic Basalt with Quartz Inclusions

Aphanitic Porphyritic Basalt

Hardness: 6-7 (Mohs); Color: dark grey to black matrix with white/clear inclusions; Luster: dull to vitreous; Structure: aphanitic (fine-grained) with phenocrysts; Cleavage: none (conchoidal fracture).

Hardness: 6-7 (Mohs)
Color: dark grey to black matrix with white/clear inclusions
Luster: dull to vitreous

Identified May 3, 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, typically at mid-ocean ridges or hotspots. The large crystals (phenocrysts) formed slowly at depth before eruption.

Uses & applications

Commonly used as crushed stone for aggregate in construction, road base, and railroad ballast. Larger pieces are sometimes used in architectural facing or as decorative garden stones.

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 extensively on the Moon and Mars.

Field identification & locations

Identified by its heavy weight, dark color, and fine-grained matrix containing visible larger crystals. Found globally in volcanic regions such as Iceland, Hawaii, and the Pacific Northwest.

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