igneous

Vesicular Basalt (Scoria)

Aphanitic Mafic Igneous Rock (Vesicular Basalt)

Hardness: 6.0; Color: Dark grey to reddish-black; Luster: Dull/Earthy; Structure: Vesicular (gas bubbles); Cleavage: None (conchoidal fracture); Specific Gravity: 2.8–3.0

Hardness: 6
Color: Dark grey to reddish-black
Luster: Dull/Earthy

Identified April 6, 2026More igneous →

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Physical properties

Hardness: 6.0; Color: Dark grey to reddish-black; Luster: Dull/Earthy; Structure: Vesicular (gas bubbles); Cleavage: None (conchoidal fracture); Specific Gravity: 2.8–3.0

Formation & geological history

Formed during explosive volcanic eruptions or on the surface of lava flows when volcanic gases expand and get trapped in cooling magma during the Cenozoic era.

Uses & applications

Used in landscaping, lightweight concrete, gas grill lava rocks, drainage systems, and as an abrasive in stone-washing textiles.

Geological facts

The holes, called vesicles, are formed by gases coming out of solution as the magma depressurizes. If a specimen has enough holes, it can occasionally float on water briefly, though less so than pumice.

Field identification & locations

Identified by its swiss-cheese appearance and high density compared to pumice. Commonly found in volcanic regions like Hawaii, Iceland, and the Pacific Northwest.

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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 - Na8(Al6Si6O24)Cl2

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Blue Apatite

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

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Magnetite

Magnetite (Fe3O4)

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