igneous

Pumice

Vesicular volcanic glass (primarily SiO2)

Hardness: 5-6 (Mohs), Color: Light gray to tan, Luster: Dull/Glassy (in thin shards), Structure: Vesicular/Amorphous, Cleavage: None, Specific Gravity: 0.25 - 0.7 (floats on water)

Identified March 19, 2026More igneous →

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Physical properties

Hardness: 5-6 (Mohs), Color: Light gray to tan, Luster: Dull/Glassy (in thin shards), Structure: Vesicular/Amorphous, Cleavage: None, Specific Gravity: 0.25 - 0.7 (floats on water)

Formation & geological history

Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is ejected into the air. The rapid cooling and depressurization trap gas bubbles, creating a frothy, glass-like texture. Typical of Rhyolitic or Andesitic eruptions.

Uses & applications

Used in personal care (exfoliating skin), industrial abrasives, lightweight concrete blocks, landscaping, and denim 'stone-washing'.

Geological facts

Pumice is the only rock that can float on water due to its incredible porosity. Immense 'pumice rafts' have been observed in the ocean following underwater volcanic eruptions, some spanning hundreds of miles.

Field identification & locations

Identify by its extremely lightweight feel and visible 'bubble' holes (vesicles). It is commonly found near volcanic activity sites like the Cascades (USA), Italy, and Iceland. Collectors should look for pieces with minimal staining and intact pore structures.

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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