Igneous

Scoria (Lava Rock)

Vesicular Basalt / Scoria

Hardness: 5-6 Mohs. Color: Dark brown to black (often weathers to dark red). Luster: Dull/Earthy. Structure: Highly vesicular (pitted with gas bubbles). Specific Gravity: Relatively low/lightweight due to air pockets.

Hardness: 5-6 Mohs
Color: Dark brown to black (often weathers to dark red)
Luster: Dull/Earthy

Identified March 31, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the rapid cooling of basaltic or andesitic lava containing high concentrations of dissolved gas. As the lava erupts, the gas expands and is trapped as the rock solidifies, creating vesicles. It is common in Cenozoic volcanic fields.

Uses & applications

Extensively used in landscaping, gas grills, high-temperature insulation, drainage systems, and as an additive in lightweight concrete. Occasionally used in bead jewelry for essential oil diffusing.

Geological facts

Unlike pumice, scoria is usually denser and will sink in water. It is a major component of volcanic cinder cones. The term scoria comes from the Greek word for 'rust.'

Field identification & locations

Identify by its 'sponge-like' appearance, dark color, and sharp, jagged edges. Found universally in volcanic regions such as Iceland, Hawaii, and the Western United States (e.g., Arizona, California).

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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