igneous

Pumice

Pumice (Vesicular volcanic glass / Rhyolite or Trachyte)

Hardness: 5-6 (Mohs); Color: white, cream, or light grey; Luster: dull/pearly; Structure: highly vesicular (pitted with air bubbles); Specific Gravity: less than 1.0 (it floats in water).

Hardness: 5-6 (Mohs)
Color: white, cream, or light grey
Luster: dull/pearly

Identified March 16, 2026More igneous →

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Physical properties

Hardness: 5-6 (Mohs); Color: white, cream, or light grey; Luster: dull/pearly; Structure: highly vesicular (pitted with air bubbles); Specific Gravity: less than 1.0 (it floats in water).

Formation & geological history

Formed during explosive volcanic eruptions where highly pressurized lava rapidly cools and depressurizes, trapping gas bubbles within the rock material as it solidifies into glass.

Uses & applications

Used as an abrasive in hygiene products (exfoliating stones, toothpaste), in construction for lightweight concrete, and as a polishing agent for metal and wood.

Geological facts

Pumice is the only rock that can float on water until it eventually becomes waterlogged and sinks. Large eruptions can create 'pumice rafts' that travel for thousands of miles across oceans.

Field identification & locations

Identify in the field by its extremely light weight and porous 'sponge-like' appearance. Commonly found near active or dormant volcanic regions like the Cascades, Mediterranean, or New Zealand.

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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

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Magnetite

Magnetite (Fe3O4)

mineral