igneous

Basalt (Vesicular or Porphyritic)

Aphanitic Mafic Igneous Rock

Hardness: 5-6 Mohs. Color: Dark grey to black with light-colored phenocrysts. Luster: Dull to sub-vitreous. Crystal structure: Fine-grained matrix (aphanitic) with larger visible crystals. Specific gravity: 2.8-3.0.

Hardness: 5-6 Mohs
Color: Dark grey to black with light-colored phenocrysts
Luster: Dull to sub-vitreous

Identified May 27, 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 surface of a terrestrial planet or moon. Most basalt on Earth is less than 200 million years old due to tectonic recycling.

Uses & applications

Used in construction as aggregate, for paving, in the manufacturing of stone wool insulation, and occasionally as decorative polished stones or for aquarium landscaping.

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 on the Moon and Mars.

Field identification & locations

Identify by dark color, heavy weight (relative to size), and fine-grained texture. Often found along coastlines or in volcanic regions like Hawaii or the Pacific Northwest.

Other igneous specimens

See all

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

Dalmatian Jasper

Aplite with Arfvedsonite inclusions

igneous

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Blue Apatite

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

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral