igneous

Pumice

Pumice (Volcanic Glass)

Hardness: 5-6 (Mohs), Color: Light gray, tan, or cream, Luster: Dull to pearly, Structure: Vesicular (highly porous/holey), Cleavage: None, Specific Gravity: 0.25-1.2 (often floats on water)

Identified May 31, 2026More igneous →

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Physical properties

Hardness: 5-6 (Mohs), Color: Light gray, tan, or cream, Luster: Dull to pearly, Structure: Vesicular (highly porous/holey), Cleavage: None, Specific Gravity: 0.25-1.2 (often floats on water)

Formation & geological history

Formed during explosive volcanic eruptions when highly pressurized, gas-rich frothy magma is ejected and cools rapidly, trapping gas bubbles in a glass matrix.

Uses & applications

Used as an abrasive in cosmetics (foot stones), heavy-duty hand soaps, polishing, lightweight concrete aggregate, and horticultural soil amendments.

Geological facts

Pumice is the only rock that can float on water until it becomes waterlogged. Huge 'pumice rafts' can form in the ocean after underwater volcanic eruptions, traveling thousands of miles.

Field identification & locations

Identify by its extremely light weight, abrasive texture, and 'sponge-like' appearance with visible pits (vesicles). Commonly found in volcanic regions like the Cascades (USA), Italy, and Iceland.

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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