igneous

Pumice

Pumice (a highly vesicular volcanic glass)

Hardness: 5-6 Mohs (though fragile due to pores); Color: White, cream, or light grey; Luster: Dull to pearly; Structure: Vesicular (full of holes/bubbles); Specific Gravity: Sub-1.0 (floats in water).

Hardness: 5-6 Mohs (though fragile due to pores)
Color: White, cream, or light grey
Luster: Dull to pearly

Identified March 26, 2026More igneous →

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Physical properties

Formation & geological history

Formed during explosive volcanic eruptions when lava is ejected into the air; rapid cooling and gas pressure create a frothy, glass-like structure. Commonly found in subduction zone volcanic regions like the Andes or Cascade Range.

Uses & applications

Used as an abrasive in cleaning supplies, polishes, and exfoliants (pumice stones). In construction, it is used as a lightweight aggregate for concrete and as a soil amendment in horticulture.

Geological facts

Pumice is the only rock that can reliably float on water for long periods of time. In 1883, after the eruption of Krakatoa, pumice rafts floated across the Indian Ocean for up to two years.

Field identification & locations

Identify by its light weight and 'sponge-like' appearance. It is found near active or extinct volcanoes; collectors should look for specimens that feel unexpectedly light for their size. If it floats in a bucket of water, it's pumice.

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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