igneous

Scoria

Extrusive Basaltic Scoria

Hardness: 5-6 Mohs. Color: Dark gray, black, reddish-brown. Luster: Dull. Texture: Highly vesicular (honeycomb-like). Crystal Structure: Aphanitic (fine-grained), often glass-dominated. Specific Gravity: 0.8 to 2.0 (often floats briefly)

Hardness: 5-6 Mohs
Color: Dark gray, black, reddish-brown
Luster: Dull

Identified January 5, 2026More igneous →

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Physical properties

Formation & geological history

Formed from gassy, mafic magma ejected during explosive volcanic eruptions. As the lava cools rapidly in the air, dissolved gases expand into bubbles (vesicles) and are trapped as the rock solidifies. Common in Cinder Cones

Uses & applications

Used in high-temperature insulation, drainage rock, gas grill 'lava rocks', landscaping, and as a lightweight aggregate in concrete

Geological facts

Scoria is technically a volcanic glass rather than a crystal. Because of its high surface area and porous nature, it was historically used by Romans as a lightweight building material for domes like the Pantheon

Field identification & locations

Identify by its lightweight feel and numerous visible holes (vesicles). Found near active or extinct volcanic cinder cones in places like Iceland, Hawaii, and the American Southwest

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