igneous

Pumice

Vesicular Rhyolite / Glassy Igneous Rock

Hardness: 5-6 (Mohs scale), but feels soft/crumbly; Color: light gray to cream/tan; Luster: dull to pearly; Crystal structure: Amorphous/Vitreous (volcanic glass); Highly vesicular (porous) with a frothy appearance; Specific gravity: < 1.0 (floats on water).

Hardness: 5-6 (Mohs scale), but feels soft/crumbly
Color: light gray to cream/tan
Luster: dull to pearly

Identified March 7, 2026More igneous →

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Physical properties

Formation & geological history

Formed through explosive volcanic eruptions. It is created when super-heated, highly pressurized molten rock is violently ejected from a volcano, cooling so rapidly that gas bubbles are trapped in a glassy matrix. Most common in young Cenozoic volcanic regions.

Uses & applications

Used in construction as lightweight aggregate/concrete, in personal care as an exfoliant (pumice stones), for stone-washing denim jeans, as an abrasive in polishing and erasers, and in horticulture for aeration.

Geological facts

Pumice is the only rock known to float on water due to its incredible porosity. After large undersea volcanic eruptions, 'pumice rafts' can form, which are floating islands of stone that can travel thousands of miles across the ocean.

Field identification & locations

Identify in the field by its light weight (low density), light color, and surface full of tiny bubbles. It is commonly found in areas of explosive silicic volcanism, such as Italy, Turkey, Greece, and the Western United States.

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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