igneous

Scoria

Extrusive Igneous Rock (Basaltic/Andesitic Composition)

Hardness: 5-6 (Mohs). Color: Dark reddish-brown, chocolate brown, or black. Luster: Dull/Earthy. Structure: Highly vesicular (porous) with large, distinct round pits. Specific Gravity: Generally high enough to sink in water, unlike pumice.

Hardness: 5-6 (Mohs)
Color: Dark reddish-brown, chocolate brown, or black
Luster: Dull/Earthy

Identified March 26, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of basaltic or andesitic lava containing high amounts of dissolved gases. As the lava erupts, gases expand to form bubbles (vesicles) which are frozen into the rock as it solidifies. Commonly associated with cinder cones.

Uses & applications

Commonly used in landscaping (lava rock), gas grills for heat retention, high-temperature insulation, drainage systems, and as an additive in lightweight concrete.

Geological facts

Scoria can be distinguished from pumice because it has larger vesicles and thicker cell walls, making it dense enough to sink in water, whereas pumice often floats.

Field identification & locations

Identify in the field by its sponge-like appearance, abrasive surface, and reddish-to-black color. It is common in volcanic regions like the Cascades (USA), Italy, and Iceland. Collectors should look for shapes that resemble 'cinders' or volcanic bombs.

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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