igneous

Pumice

Vesicular volcanic glass (primarily SiO2)

Hardness: 5-6 Mohs (though fragile); Color: light gray, cream, or pale tan; Luster: dull to pearly; Structure: highly vesicular (full of gas bubbles); Specific Gravity: < 1.0 (floats in water).

Hardness: 5-6 Mohs (though fragile)
Color: light gray, cream, or pale tan
Luster: dull to pearly

Identified March 20, 2026More igneous →

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Physical properties

Hardness: 5-6 Mohs (though fragile); Color: light gray, cream, or pale tan; Luster: dull to pearly; Structure: highly vesicular (full of gas bubbles); Specific Gravity: < 1.0 (floats in water).

Formation & geological history

Formed during explosive volcanic eruptions when magma is rapidly depressurized and quenched, trapping gas bubbles. Associated with silicic lavas (rhyolite, dacite). Geological age varies by location (Recent to Cenozoic).

Uses & applications

Abrasives (pumice stones), lightweight concrete aggregate, horticultural soil amendments, and stone-washing textiles (distressing denim).

Geological facts

Pumice is the only rock that consistently floats until it becomes waterlogged. Large eruptions can create 'pumice rafts' several kilometers long that drift across the ocean for years.

Field identification & locations

Identify in the field by its extreme lightness, frothy texture, and ability to float in water. Commonly found in volcanic regions like the Cascades (USA), Italy, and 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