igneous
Pumice or vesicular volcanic tuff
Pumice: highly vesicular volcanic glass, chiefly rhyolitic to dacitic; possible tuff: lithified ash and pumice fragments
AI-generated identification · may be incorrectLight tan, porous, fine-grained specimen with abundant cavities and dark mineral specks; likely hardness about 5–6 for pumice glass, with poor cleavage, dull to silky luster, and low specific gravity. It may float if sufficiently vesicular.
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Physical properties
Light tan, porous, fine-grained specimen with abundant cavities and dark mineral specks; likely hardness about 5–6 for pumice glass, with poor cleavage, dull to silky luster, and low specific gravity. It may float if sufficiently vesicular.
Formation & geological history
Forms when gas-rich lava explosively erupts and rapidly cools, trapping bubbles; tuff forms when ash and pumice fragments lithify. Such material can range from recent volcanic deposits to any age, but the specimen’s age cannot be determined visually.
Uses & applications
Used as an abrasive, lightweight aggregate, soil-aeration material, concrete additive, and landscaping stone; selected pieces are sold as curios or grooming stones.
Geological facts
Pumice is volcanic glass rather than a rock made of large crystals; its extreme vesicularity records rapid decompression and cooling during explosive eruptions.
Field identification & locations
Check whether it is unusually lightweight, porous, and possibly buoyant; a streak or acid test is generally unhelpful. Common sources include Iceland, Italy, the western United States, Mexico, and New Zealand.
