igneous
Vesicular quartz-rich rock, possibly weathered rhyolite or silicified volcanic breccia
Silica-rich volcanic rock; likely microcrystalline quartz (SiO₂) with altered feldspar and iron-oxide staining
AI-generated identification · may be incorrectGray to brown, dull-to-waxy luster, irregular cavities (vesicles or weathering voids), and massive cryptocrystalline texture; quartz hardness is about 7 Mohs, but the whole altered specimen may be softer and porous. No clear cleavage is visible; density is variable because of the cavities.
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Physical properties
Gray to brown, dull-to-waxy luster, irregular cavities (vesicles or weathering voids), and massive cryptocrystalline texture; quartz hardness is about 7 Mohs, but the whole altered specimen may be softer and porous. No clear cleavage is visible; density is variable because of the cavities.
Formation & geological history
Likely formed from silica-rich volcanic lava or fragmental volcanic material, later altered and weathered, with iron oxides producing the brown-gold staining. The exact age cannot be determined from the photograph; such rocks range from Precambrian to recent volcanic settings.
Uses & applications
Mostly a collector or decorative specimen; fresh rhyolite can be used as aggregate or building stone, but this porous piece has little industrial value and is unsuitable for most construction.
Geological facts
The holes may represent gas bubbles, dissolved mineral pockets, or weathered-out carbonate/zeolite fillings rather than true pumice vesicles.
Field identification & locations
Commonly found in volcanic terrains, especially areas with hydrothermal alteration. A glassy streak, conchoidal fracture, or quartz-rich hardness supports silicification; acid testing and a hand lens help distinguish it from limestone or slag.
