igneous

Pumice

Pumice (Vesicular Felsic Glass)

Hardness: 5-6 Mohs (though fragile), Color: light gray to tray-white, Luster: dull to silky, Crystal Structure: amorphous glass (non-crystalline), Specific Gravity: 0.25-0.9 (floats on water), highly vesicular.

Identified May 17, 2026More igneous →

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Physical properties

Formation & geological history

Formed during explosive volcanic eruptions when highly pressurized, silica-rich lava is violently ejected. The rapid cooling and depressurization freeze gas bubbles in the petrifying lava. Generally found in Quaternary to modern volcanic deposits.

Uses & applications

Used as a lightweight aggregate in concrete, as an abrasive in polishing compounds, stone-washing textiles (jeans), and in cosmetic products (exfoliating skin).

Geological facts

Pumice is the only rock that consistently floats on water due to its air-filled pores. Large eruptions can create 'pumice rafts' that can travel across oceans for years.

Field identification & locations

Identify by its extremely lightweight feel and sponge-like, porous texture with glass-sharp edges. Found in areas with history of explosive volcanism like the Andes, Cascades, or Mediterranean.

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