igneous
Vesicular volcanic rock, likely pumice or scoriaceous rhyolite
Vesicular rhyolite/dacite; predominantly volcanic glass and feldspar, with iron-oxide staining
AI-generated identification · may be incorrectHardness about 5–6 Mohs; cream to pink-brown, highly porous, dull to slightly vitreous luster, and no visible cleavage. The abundant rounded cavities indicate vesicles formed by escaping gas.
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Physical properties
Hardness about 5–6 Mohs; cream to pink-brown, highly porous, dull to slightly vitreous luster, and no visible cleavage. The abundant rounded cavities indicate vesicles formed by escaping gas.
Formation & geological history
Formed when gas-rich silica-rich lava cooled rapidly at or near the surface, commonly during explosive eruptions; its exact geological age cannot be determined from the photograph. The reddish coloration likely reflects oxidation of iron-bearing minerals.
Uses & applications
Pumice is used as an abrasive, lightweight aggregate, horticultural medium, and concrete additive; attractive pieces are inexpensive specimens. It has little jewelry value unless unusually patterned or polished.
Geological facts
Its low density and abundant vesicles distinguish it from most dense volcanic rocks; pumice may float initially, whereas scoria is generally darker and denser.
Field identification & locations
Look for a very lightweight, frothy texture, sharp glassy walls around cavities, and possible flotation; test density and avoid assuming identification from color alone. Common in volcanic regions worldwide, including the western United States, Italy, Iceland, and New Zealand.
