igneous

Vesicular Basalt (Iron-Stained)

Mafic Volcanic Rock (Basalt)

Hardness: 5-6 Mohs. Color: Reddish-brown to tan surface due to oxidation, dark gray interior. Luster: Dull/Earthy. Structure: Aphanitic with vesicular texture (voids). Specific gravity: 2.8-3.0.

Hardness: 5-6 Mohs
Luster: Dull/Earthy

Identified May 8, 2026More igneous →

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Physical properties

Hardness: 5-6 Mohs. Color: Reddish-brown to tan surface due to oxidation, dark gray interior. Luster: Dull/Earthy. Structure: Aphanitic with vesicular texture (voids). Specific gravity: 2.8-3.0.

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. The pits (vesicles) were created by gas bubbles escaping as the lava solidified. Typical of Cenozoic volcanic activity.

Uses & applications

Used in landscaping, as a construction aggregate, for railroad ballast, and sometimes in stone masonry. Smaller vesicular pieces are often marketed as 'lava rock' for grills.

Geological facts

The reddish color is caused by the oxidation of iron-bearing minerals within the rock, essentially 'rusting' the surface over time. This process is common in humid or surface-exposed environments.

Field identification & locations

Identify by the presence of small holes (vesicles) and high density despite the pits. Commonly found in volcanic fields, oceanic islands, and near tectonic plate boundaries. Use a hand lens to look for tiny basaltic crystals.

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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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)

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Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral