igneous

Pumice

Pumicite (Amorphous Volcanic Glass)

Hardness: 5-6 (Mohs), though brittle; Color: white, cream, tan, or grey; Luster: vitreous to pearly (silky); Structure: highly vesicular (full of gas bubbles); Cleavage: none; Specific Gravity: 0.25 to 0.7 (floats in water).

Hardness: 5-6 (Mohs), though brittle
Color: white, cream, tan, or grey
Luster: vitreous to pearly (silky)

Identified February 21, 2026More igneous →

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Physical properties

Formation & geological history

Formed during explosive volcanic eruptions when high-pressure, gas-rich magma is ejected and cools rapidly, trapping gas bubbles. Often found in pyroclastic deposits from the Cenozoic era to the present.

Uses & applications

Used as an abrasive in hand soaps (Lava soap), exfoliating stones, and dental polishing. Also used in light-weight concrete, horticultural soil amendments, and stonewashing denim jeans.

Geological facts

Pumice is the only rock that can float on water due to its low density and air-filled pores. Large eruptions can create 'pumice rafts' in the ocean that travel for thousands of miles.

Field identification & locations

Identify in the field by its light weight (it should feel lighter than it looks) and its vesicular, sponge-like texture. Common in volcanic regions like the Cascades, Italy, or Iceland. If it's very light and floats, it's pumice.

Other igneous specimens

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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