Pumice
Vitreous Volcanic Rock (Pumice) · Collector Mineral / Decorative Stone / Industrial Mineral
Crystal System
Amorphous (Non-crystalline glass); habit is vesicular, frothy, or pumiceous
Mineral Group
Volcanic Glass / Silicate-rich Igneous Rock
Chemical Formula
Variable (Complex Silicate Glass); typically 70% or more SiO2 with Al2O3, Fe2O3, and Na2O/K2O
Formation Process
Igneous (Volcanic); formed during explosive volcanic eruptions when highly pressurized, gas-rich silicic magma is violently ejected and cools rapidly, trapping gas bubbles (vesicles) as it solidifies.
About This Crystal
A lightweight, highly vesicular volcanic glass. The specimen appears light gray to tan with a dull, earthy to pearly luster. It is characterized by a frothy, sponge-like texture with numerous visible pores (vesicles). It is opaque to translucent on thin edges.
Physical Characteristics
Color: Creamy white to light gray; Streak: White; Cleavage: None; Fracture: Conchoidal (on a microscopic scale) to uneven; Specific Gravity: 0.25 to 0.9 (floats on water); Fluorescence: Usually inert.
Optical Properties
Refractive Index: Approximately 1.48 to 1.50 (for the glass phase); Isotropic; No birefringence or pleochroism due to amorphous structure.
Hardness & Durability
Origin Region
Active or dormant volcanic regions globally; notable sources include Mount Pinatubo (Philippines), Aeolian Islands (Italy), and the Cascade Range (USA)
Hardness & Durability
Mohs hardness: 5.0 to 6.0; Toughness: Very brittle/fragile due to high porosity; Low wearability for jewelry but high abrasive durability.
Care & Maintenance
Care: Rinse with warm soapy water to remove dust from pores; avoid chemicals that can leach into vesicles. Storage: Store in a dry place; fragile structure can crumble under pressure or impact.
Rarity & Value
Common; very low financial value per specimen. Value is driven by industrial utility (abrasive, construction) rather than gemological rarity. Usually untreated.
Special Characteristics
Highly buoyant (low density allows it to float on water until water-logged); extremely high porosity; thermal and acoustic insulation properties.
Lore & History
Historically used by Romans/Greeks for stone-washing textiles, as an abrasive for exfoliation, and in the production of lightweight concrete (as seen in the Pantheon). Metaphysically associated with the throat chakra and believed to assist in 'releasing' or diffusing emotional blockages.