igneous

Pumice

Pumice (Highly vesicular volcanic glass)

Hardness: 5-6 Mohs (though fragile due to air pockets); Color: White, cream, gray, or light brown; Luster: Dull to pearly; Structure: Vesicular (full of tiny holes); Specific Gravity: 0.25-0.9 (Floats in water).

Hardness: 5-6 Mohs (though fragile due to air pockets)
Color: White, cream, gray, or light brown
Luster: Dull to pearly

Identified March 29, 2026More igneous →

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Physical properties

Formation & geological history

Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected and cools rapidly. It has occurred throughout geological history, notably in the Cenozoic era. The gas bubbles are 'frozen' in the rock, creating its unique porous structure.

Uses & applications

Used in construction for lightweight concrete, in personal care as an exfoliant (pumice stones), as an abrasive in industrial polishing, and in horticulture to improve soil drainage.

Geological facts

Pumice is the only rock that can float on water until it eventually becomes waterlogged and sinks. Large eruptions can create 'pumice rafts' that float across oceans for thousands of miles.

Field identification & locations

Identify in the field by its extremely light weight and glass-like, porous texture; if it floats in a puddle, it is pumice. Commonly found near convergent plate boundaries and areas with active or dormant volcanoes like Italy, Greece, and the Western USA.

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