Igneous

Scoria (Lava Rock)

Scoria (Vesicular Basaltic Rock)

Hardness: 5-6 (Mohs scale); Color: Dark reddish-brown to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) with large vesicles (gas pockets); Cleavage: None; Specific Gravity: Low (often floats in water initially but sinks once saturated).

Hardness: 5-6 (Mohs scale)
Color: Dark reddish-brown to black
Luster: Dull to sub-metallic

Identified February 18, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of basaltic or andesitic lava containing high concentrations of dissolved gases. As the pressure drops during an eruption, the gases expand and create bubbles (vesicles) that are trapped as the lava solidifies. Found primarily in volcanic cinder cones and flow surfaces.

Uses & applications

Used widely in landscaping (lava rock), gas grills for heat retention, lightweight concrete aggregate, high-temperature insulation, and as an abrasive in stone-washing textiles.

Geological facts

Scoria is the primary component of cinder cones, which are the most common type of volcano. Unlike pumice, which is also vesicular, scoria is denser and usually dark-colored due to its higher iron and magnesium content.

Field identification & locations

Identify in the field by its sponge-like or honeycomb appearance, rough/sharp edges, and reddish-brown to black color. Common in volcanic regions such as Hawaii, Iceland, and the American Southwest. Collectors should look for intact vesicles and iridescent coatings.

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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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Apatite (Group), Ca5(PO4)3(F,Cl,OH)

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Magnetite

Magnetite (Fe3O4)

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