igneous

Pumice

Pumice (Amorphous volcanic glass)

Hardness: 5-6 (Mohs), Color: White, cream, or light grey, Luster: Vitreous to dull, Crystal Structure: Amorphous (non-crystalline), Specific Gravity: 0.25-0.90 (highly vesicular and floats on water)

Identified May 29, 2026More igneous →

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Physical properties

Hardness: 5-6 (Mohs), Color: White, cream, or light grey, Luster: Vitreous to dull, Crystal Structure: Amorphous (non-crystalline), Specific Gravity: 0.25-0.90 (highly vesicular and floats on water)

Formation & geological history

Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected into the air; rapid cooling and depressurization create a foamy texture. Usually associated with rhyolitic or dacitic eruptions.

Uses & applications

Used as an abrasive in polishing, skin exfoliation (pumice stones), construction (lightweight 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 high porosity and trapped gas bubbles. After major eruptions, floating pumice rafts can drift on the ocean for years, sometimes covering thousands of square miles.

Field identification & locations

Identify by its extremely light weight, frothy 'sponge-like' appearance, and ability to float. Commonly found in volcanic regions such as the Ring of Fire or areas with historic ash deposits.

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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