igneous
Pumice
Pumicite
Hardness: 5-6 (but very brittle); Color: Tan, grey, or cream; Luster: Pearly to dull; Crystal structure: Amorphous (volcanic glass); Specific gravity: 0.2-0.9 (floats in water); Cleavage: None
- Hardness
- 5-6 (but very brittle)
- Color
- Tan, grey, or cream
- Luster
- Pearly to dull
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Physical properties
Hardness: 5-6 (but very brittle); Color: Tan, grey, or cream; Luster: Pearly to dull; Crystal structure: Amorphous (volcanic glass); Specific gravity: 0.2-0.9 (floats in water); Cleavage: None
Formation & geological history
Formed during violent volcanic eruptions when highly pressurized, gas-rich magma is ejected. The rapid cooling and depressurization trap gas bubbles, creating a vesicular texture. Usually found in Cenozoic volcanic regions.
Uses & applications
Used as an abrasive in soaps, pencil erasers, and stone-washing jeans. In construction, used as a lightweight aggregate for concrete and landscaping. Also used in horticulture to aerate soil.
Geological facts
Pumice is the only rock that can float on water due to its extremely high porosity. Large 'pumice rafts' have been known to float in the ocean for years after major eruptions.
Field identification & locations
Identify by its 'sponge-like' appearance and light weight. In the field, look for volcanic deposit fields. It will feel scratchy and much lighter than a standard stone of the same size.
