igneous
Pumice (Vesicular Lava)
Pumice
Hardness: 5-6 (overall rock toughness varies due to porosity), Color: Light gray to off-white, Luster: Dull to vitreous, Crystal Structure: Amorphous/glassy texture (aphanitic to vesicular), Specific Gravity: <1.0 (often floats on water due to trapped air pockets)
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Physical properties
Hardness: 5-6 (overall rock toughness varies due to porosity), Color: Light gray to off-white, Luster: Dull to vitreous, Crystal Structure: Amorphous/glassy texture (aphanitic to vesicular), Specific Gravity: <1.0 (often floats on water due to trapped air pockets)
Formation & geological history
Formed during explosive volcanic eruptions when highly gas-charged, felsic to intermediate magma cools rapidly, trapping gas bubbles as vesicles before crystallization can occur.
Uses & applications
Used as an abrasive in polishing materials, body scrubs, foot stones, lightweight aggregate in concrete, and soil amendment in horticulture.
Geological facts
Pumice is the only rock that can naturally float on water because its sponge-like structure traps gas bubbles within closed vesicles. Massive rafts of pumice can float on the ocean for thousands of miles following volcanic eruptions.
Field identification & locations
Identified by its extremely lightweight feel, porous porous vesicular texture, light gray color, and ability to float on water. Commonly found on beaches near active or historical volcanic areas like Hawaii, Iceland, and the Mediterranean.
