igneous

Scoria (often called Lava Rock)

Vesicular Basalt / Scoria

Hardness: 5-6 (Mohs scale), Color: Dark brown, black, or reddish-purplish, Luster: Dull/Sub-metallic, Structure: Highly vesicular (honeycombed with gas bubbles), Cleavage: None, Specific Gravity: 2.5–3.0 (though it feels light due to air pockets)

Identified March 15, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the cooling of mafic magma (rich in magnesium and iron). As lava erupts, trapped gases expand to form bubbles; when the lava solidifies rapidly, these holes (vesicles) are frozen in place. Common in Cenozoic era volcanic fields.

Uses & applications

Used extensively in landscaping, gas grill rocks, high-temperature insulation, concrete aggregate for lightweight blocks, and sometimes in stone-wash treatments for denim.

Geological facts

Unlike pumice, which is also vesicular, scoria is denser and usually sinks in water because it has larger vesicles and thicker cell walls. It often contains microscopic crystals of pyroxene and plagioclase feldspar.

Field identification & locations

Identify by its 'sponge-like' appearance, dark color, and sharp, jagged edges. Found near cinder cones and volcanic vents in regions like Iceland, Hawaii, and the Western USA. Collectors should look for unique oxidation patterns (the orange/rust spots seen on this specimen).

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