igneous

Scoria

Scoria (Extrusive Volcanic Rock)

Hardness: 5-6 (Mohs); Color: dark red, brownish-black, or purple; Luster: dull to earthy; Structure: highly vesicular (basaltic glass containing numerous bubbles); Specific Gravity: 0.8-2.1.

Hardness: 5-6 (Mohs)
Color: dark red, brownish-black, or purple
Luster: dull to earthy

Identified May 29, 2026More igneous →

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Physical properties

Hardness: 5-6 (Mohs); Color: dark red, brownish-black, or purple; Luster: dull to earthy; Structure: highly vesicular (basaltic glass containing numerous bubbles); Specific Gravity: 0.8-2.1.

Formation & geological history

Formed when magma containing abundant dissolved gas flows from a volcano; as the pressure is released, the gases expand and form bubbles that are frozen in place as the rock cools rapidly. Typically associated with Cenozoic volcanic activity.

Uses & applications

Used widely in landscaping, drainage, insulation, and as a high-temperature additive in gas grills (lava rock). Also used in lightweight concrete and road construction.

Geological facts

Unlike pumice, scoria has larger vesicles and thicker cell walls, which usually causes it to sink in water. It is a common component of cinder cones.

Field identification & locations

Identify by its dark color, rough texture, and abundance of small holes (vesicles). Look for it in volcanic fields or near cinder cones. Collectors should look for unique color variants or crystalline inclusions.

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