igneous

Scoria (Lava Rock)

Scoria (highly vesicular extrusive igneous rock)

Hardness: 5-6 (Mohs scale), Color: Dark red to reddish-brown (oxidized iron), Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), Cleavage: None, Specific Gravity: 2.5-3.0 (though it often feels lighter due to air pockets)

Identified March 31, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of gas-rich basaltic or andesitic lava. As the lava is ejected during a volcanic eruption, gas bubbles (vesicles) are trapped as the rock solidifies. Most specimens are relatively young geologically (Cenozoic era).

Uses & applications

Commonly used in landscaping and garden mulch for its decorative color and water retention. Used in high-temperature insulation, gas grills (lava rocks), lightweight concrete, and road traction on snowy surfaces.

Geological facts

Unlike pumice, which is also vesicular, scoria typically has larger holes, thicker walls, and is dense enough to sink in water. Its red color is usually due to the oxidation of iron within the lava as it reacts with the atmosphere.

Field identification & locations

Identify by its highly porous, honeycomb-like texture and rough, abrasive surface. It is very light for its size but usually does not float. Commonly found in volcanic fields such as those in Iceland, Hawaii, the Canary Islands, and the western United States.

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