igneous

Pumice

Pumice (Vesicular volcanic glass)

Hardness: 5-6 Mohs (though fragile), Color: light gray, cream, or pale green, Luster: dull to pearly, Structure: highly vesicular (full of holes), Cleavage: none, Specific Gravity: 0.25 to 0.70 (often floats on water).

Identified March 15, 2026More igneous →

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Physical properties

Formation & geological history

Formed during explosive volcanic eruptions when highly pressurized, gas-rich silica magma is violently ejected. Rapid cooling and depressurization trap gas bubbles, creating a frothy glass structure. Found in volcanic arcs and continental settings.

Uses & applications

Used as an abrasive in facial scrubs and foot stones, in stone-washing jeans, as a lightweight aggregate in concrete, and as a soil amendment in horticulture to improve drainage and aeration.

Geological facts

Pumice is the only rock that can float on water due to its incredible porosity. In massive eruptions, large 'pumice rafts' can form on the ocean and drift for miles, sometimes transporting marine life across oceanic basins.

Field identification & locations

Identify by its extremely light weight, frothy texture, and inability to see individual mineral crystals (glassy). Common in Italy, Turkey, Greece, and parts of the western USA (Cascade Range). Collectors look for specimens with large, unbroken vesicles.

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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