igneous

Scoria (Lava Rock)

Scoria (Extrusive Igneous Rock / Mafic Silicates)

Hardness: 5-6 Mohs. Color: Dark brown, black, or reddish-brown. Luster: Dull/Earthy. Structure: Vesicular (highly porous with gas bubbles). Cleavage: None. Specific Gravity: Generally less than 2.0 (often feels very light but does not float like pumice).

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

Identified February 26, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the cooling of gas-rich mafic magma (basaltic or andesitic). As magma is ejected during explosive volcanic eruptions, the sudden drop in pressure causes dissolved gases to expand into bubbles, which are trapped as the lava solidifies.

Uses & applications

Commonly used in landscaping (volcanic mulch), high-temperature insulation, gas grills (lava rocks), lightweight concrete aggregate, and as a drainage material in horticulture.

Geological facts

Unlike pumice, scoria usually has a basaltic composition and larger vesicle (bubble) walls, which makes it denser than water, so it typically sinks. It is a signature product of cinder cone volcanoes.

Field identification & locations

Identify in the field by its sponge-like appearance and sharp, abrasive edges. Commonly found in volcanic fields such as those in Iceland, Italy, the Canary Islands, and the Western United States (Arizona, New Mexico).

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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)

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Magnetite

Magnetite (Fe3O4)

mineral