mineral
Botryoidal quartz (likely chalcedony/agate)
Microcrystalline silica, SiO₂; possibly quartz-rich chalcedony with iron-oxide staining
AI-generated identification · may be incorrectWhite to cream, rounded botryoidal (“grape-like”) masses with dull to waxy luster and brown-red inclusions. Quartz hardness is about 7 Mohs, lacks cleavage, has conchoidal fracture, and specific gravity near 2.6; the image is too blurred for certainty.
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Physical properties
White to cream, rounded botryoidal (“grape-like”) masses with dull to waxy luster and brown-red inclusions. Quartz hardness is about 7 Mohs, lacks cleavage, has conchoidal fracture, and specific gravity near 2.6; the image is too blurred for certainty.
Formation & geological history
Forms when silica-rich groundwater precipitates in cavities, fractures, or vesicles, commonly replacing or coating volcanic rock. Usually Cenozoic to older, depending on its host deposit.
Uses & applications
Used as an ornamental and lapidary material; attractive pieces may be polished or cut as cabochons. Ordinary specimens have little industrial value beyond silica content.
Geological facts
The rounded growths are called botryoidal texture and result from repeated silica deposition around nucleation points; iron oxides commonly create the rusty brown coloration.
Field identification & locations
Look for translucent edges, waxy luster, conchoidal fracture, and hardness sufficient to scratch glass; acid should not visibly react. Common sources include volcanic terrains in Brazil, Uruguay, Mexico, India, and the western United States.
