igneous

Pumice

Pumice (Amorphous volcanic glass)

Hardness: 5-6 (but very friable); Color: White, cream, or light grey; Luster: Dull to pearly; Structure: Vesicular (highly porous); Specific Gravity: 0.25 to 0.9 (floats in water).

Hardness: 5-6 (but very friable)
Color: White, cream, or light grey
Luster: Dull to pearly

Identified May 7, 2026More igneous →

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Physical properties

Hardness: 5-6 (but very friable); Color: White, cream, or light grey; Luster: Dull to pearly; Structure: Vesicular (highly porous); Specific Gravity: 0.25 to 0.9 (floats in water).

Formation & geological history

Formed during explosive volcanic eruptions when high-pressure, gas-charged molten rock is ejected and cools rapidly, trapping gas bubbles in a frothy glass structure.

Uses & applications

Used as an abrasive in toothpaste and cosmetics (exfoliants), in construction for lightweight concrete, in horticulture as a soil amendment, and for stone-washing denim.

Geological facts

Pumice is the only rock that consistently floats on water due to its incredible number of vacuum-sealed air cells. Huge 'pumice rafts' can form in the ocean after underwater volcanic eruptions.

Field identification & locations

Identify in the field by its extreme lightness (low density) and distinct sponge-like, bubbly appearance. Look for it near felsic volcanic vents or washed up on coastlines.

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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