igneous

Pumice

Pumice (Amorphous volcanic glass)

Hardness: 5-6 on Mohs scale (but brittle due to vesicular structure); Color: White, cream, or light grey; Luster: Pearly to dull; Texture: Vesicular (highly porous/full of air bubbles); Specific Gravity: 0.25 to 1.2 (often floats on water).

Hardness: 5-6 on Mohs scale (but brittle due to vesicular structure)
Color: White, cream, or light grey
Luster: Pearly to dull

Identified March 22, 2026More igneous →

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Physical properties

Formation & geological history

Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected. The rapid cooling and depressurization trap gas bubbles as the rock solidifies. It is found in volcanic regions of all geological ages, especially those with high silica (rhyolitic) volcanism.

Uses & applications

Used as an abrasive in soaps (pumice stones) and polishes; in horticulture to aerate soil; in construction as a lightweight aggregate for concrete blocks; and in textiles for stone-washing denim.

Geological facts

Pumice is the only rock that can float on water, sometimes creating 'pumice rafts' in the ocean that can float for miles and last for years after an eruption. It is essentially frozen volcanic foam.

Field identification & locations

Identify by its extremely light weight and 'frothy' appearance full of tiny holes. Found near active or extinct explosive volcanoes (e.g., Cascades in USA, Italy, Greece). Collectors look for specimens with large vesicles or unique colors.

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