igneous

Basalt with Iron Oxidation

Extrusive Mafic Igneous Rock (composed of Plagioclase and Pyroxene)

Hardness: 6 (Mohs scale); Color: Dark grey to black matrix with yellowish-brown limonite/goethite staining; Luster: Dull/Earthy; Structure: Fine-grained aphanitic with small vesicles (holes from gas bubbles).

Hardness: 6 (Mohs scale)
Luster: Dull/Earthy

Identified January 28, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a planet or moon. The yellowish-orange surface is due to chemical weathering where iron-rich minerals oxidize over time.

Uses & applications

Used extensively in construction as crushed stone for road base, concrete aggregate, railroad ballast, and in the production of high-strength stone wool insulation.

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, forming the dark lunar 'maria'.

Field identification & locations

Identify by its heavy weight (high specific gravity), fine-grained texture, and dark color often masked by rusty oxidation. Commonly found in volcanic fields or near oceanic rifts.

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