igneous

Scoria (Lava Rock)

Scoria

Hardness: 5-6 (Mohs scale), Color: Dark brown, black, or reddish-purple, Luster: Dull (sub-vitreous), Crystal Structure: Amorphous/Aphanitic, Cleavage: None, Specific Gravity: 0.8-2.1 (often light enough to nearly float, but usually sinks)

Identified May 17, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of basaltic or andesitic magma. As the pressure drops during an eruption, dissolved gases expand to create bubbles (vesicles) which are frozen in place as the rock solidifies.

Uses & applications

Used in landscaping, gas grills, high-temperature insulation, drainage rock, and as an abrasive in stone-washing jeans.

Geological facts

The vesicles in scoria are much larger and thicker-walled than those in pumice. Unlike most pumice, the higher iron content causes scoria to be denser and usually too heavy to float in water.

Field identification & locations

Identify by its highly vesicular (bubbly) texture and dark color. It is common in regions with active or dormant volcanic activity such as Iceland, Hawaii, and the Canary Islands.

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