Pumice

Hardness: 5-6 (but brittle), Color: light gray to cream, Luster: dull to pearly, Structure: highly vesicular (bubbly), Specific gravity: <1 (floats in water)

Formed during explosive volcanic eruptions when gas-rich silicic magma cools rapidly. The trapped gas bubbles create a frothy, cellular structure. Found in volcanic arcs and active boundary zones.

Abrasive in soaps and polishes, horticulture (soil aeration), lightweight concrete aggregate, and stone-washing textiles (jeans).

Pumice is the only rock that can float on water due to its air-filled vesicles. It is essentially volcanic glass froth.

Identify by its extremely light weight, abrasive texture, and hundreds of tiny visible pores. Check if it floats; no other common rock does. Found in regions of recent volcanic activity like Italy, Iceland, and the western USA.