igneous

Scoria

Vesicular Basalt / Scoriaceous Basalt

Hardness: 5-6 (Mohs scale); Color: Black, dark gray, or reddish-brown; Luster: Dull/Sub-metallic; Crystal Structure: Aphanitic (fine-grained matrix); Cleavage: None; Specific Gravity: 1.0 - 2.0 (porous and lightweight).

Hardness: 5-6 (Mohs scale)
Color: Black, dark gray, or reddish-brown
Luster: Dull/Sub-metallic

Identified March 15, 2026More igneous →

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Physical properties

Formation & geological history

Formed from extrusive volcanic eruptions where magma containing trapped gases is expelled into the air or flows on the surface. Rapid cooling and gas expansion create the vesicular (pitted) texture. Found in volcanic regions like Hawaii, Iceland, and the Andes.

Uses & applications

Commonly used in landscaping (lava rocks), high-temperature insulation, lightweight concrete aggregate, drainage systems, and as an abrasive in 'stone-washed' jeans.

Geological facts

Scoria is often mistaken for pumice, but scoria is more dense and darker in color. Unlike some pumice, scoria is usually too heavy to float in water because of its basaltic composition and larger vesicle walls.

Field identification & locations

Identify by its 'Swiss cheese' appearance, dark color, and rough, sharp edges. Commonly found on the slopes of cinder cone volcanoes. Collectors look for pieces with iridescent coatings or large, unbroken air pockets.

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