igneous

Vesicular Basalt (Scoria)

Basalt (Extrusive Igneous Rock)

Hardness: 5-6 Mohs. Color: Black, dark gray, or reddish-brown. Luster: Dull to sub-metallic. Crystal structure: Aphanitic (fine-grained) with a vesicular (pitted) texture. Specific gravity: 2.8-3.0.

Hardness: 5-6 Mohs
Color: Black, dark gray, or reddish-brown
Luster: Dull to sub-metallic

Identified May 18, 2026More igneous →

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Physical properties

Hardness: 5-6 Mohs. Color: Black, dark gray, or reddish-brown. Luster: Dull to sub-metallic. Crystal structure: Aphanitic (fine-grained) with a vesicular (pitted) texture. Specific gravity: 2.8-3.0.

Formation & geological history

Formed during explosive volcanic eruptions or from the cooling of gas-rich lava flows. As the lava cools rapidly on the surface, trapped gas bubbles (vesicles) form the characteristic holes. It can be found in volcanic regions of any geological age, from modern flows to ancient Precambrian belts.

Uses & applications

Used in landscaping as decorative lava rock, as an aggregate in gas grills to retain heat, in concrete lightweight aggregate, and occasionally in road construction. High-quality specimens are kept in mineral collections.

Geological facts

The holes in vesicular basalt can sometimes be filled with secondary minerals like zeolites, quartz, or calcite, turning the rock into 'amygdaloidal basalt.' This specific specimen appears to have significant internal mineralization or a contact zone with lighter rhyolitic material.

Field identification & locations

Identified by its dark color, heavy weight (relative to pumice), and presence of frequent gas bubbles or vesicles. Commonly found in volcanic fields like those in Iceland, Hawaii, or the Cascade Range. Field collectors should look for basaltic flows near cinder cones.

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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.

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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)

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Magnetite

Magnetite (Fe3O4)

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