igneous

Vesicular Basalt (Scoria)

Extrusive Mafic Igneous Rock (primarily Plagioclase Feldspar and Pyroxene)

Hardness: 5-6 Mohs. Color: Dark gray, black, or reddish-brown due to iron oxidation. Luster: Dull to sub-metallic. Crystal structure: Aphanitic (fine-grained) with a vesicular (pitted) texture. Specific Gravity: 2.8-3.0 (though it may feel lighter due to air pockets).

Hardness: 5-6 Mohs
Color: Dark gray, black, or reddish-brown due to iron oxidation
Luster: Dull to sub-metallic

Identified February 22, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava (basaltic) expelled from a volcano. The 'holes' or vesicles are created by gas bubbles trapped in the lava as it solidifies. These rocks are common in Cenozoic volcanic fields.

Uses & applications

Widely used in landscaping (lava rocks), heat-resistant barbecue liners, lightweight concrete aggregate, high-friction road base, and acoustic insulation.

Geological facts

Vesicular basalt is the most common rock type on the surfaces of Earth, the Moon, and Mars. If the vesicles make up more than 50% of the rock's volume, it is specifically referred to as Scoria.

Field identification & locations

Identify in the field by its distinctive 'swiss cheese' appearance and dark color. It is commonly found in volcanic regions like Hawaii, Iceland, and the Pacific Northwest. Collectors look for pieces with unique colorful oxidation or mineral secondary fillings (amygdules).

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