igneous

Pumice

Pumice (Vesicular volcanic glass)

Hardness: 5-6 (Mohs), Color: Cream, white, or light gray, Luster: Dull/pearly, Structure: Highly vesicular/frisky glass, Cleavage: None, Specific Gravity: 0.25 to 0.7 (floats on water)

Identified May 25, 2026More igneous →

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Physical properties

Hardness: 5-6 (Mohs), Color: Cream, white, or light gray, Luster: Dull/pearly, Structure: Highly vesicular/frisky glass, Cleavage: None, Specific Gravity: 0.25 to 0.7 (floats on water)

Formation & geological history

Formed during explosive volcanic eruptions when highly pressurized, gas-rich magma is violently ejected and cools rapidly, trapping gas bubbles as vesicles. Found in subduction zones worldwide.

Uses & applications

Used as an abrasive in soaps and cleaners, in horticultural soil mixes, for stonewashing denim, and as a lightweight aggregate in concrete.

Geological facts

Pumice is the only rock that can float on water due to its air-filled pores. It has been used since ancient times for hygiene; the Romans used it in construction to make lightweight dome structures like the Pantheon.

Field identification & locations

Identify in the field by its sponge-like appearance and extremely light weight. If it floats in a puddle, it is pumice. Look for it near active or dormant volcanic regions and beaches where it may have washed ashore.

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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