mineral
Tumbled agate and jasper specimens
Chalcedony (microcrystalline quartz, SiO₂), including agate and jasper varieties
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; waxy to vitreous luster, opaque to translucent, with brown, tan, gray, and reddish colors. The upper piece shows possible agate-like chalcedony veining; the darker pieces may be jasper or iron-stained chalcedony, but exact identification requires testing.
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Physical properties
Hardness about 6.5–7 Mohs; waxy to vitreous luster, opaque to translucent, with brown, tan, gray, and reddish colors. The upper piece shows possible agate-like chalcedony veining; the darker pieces may be jasper or iron-stained chalcedony, but exact identification requires testing.
Formation & geological history
Formed when silica-rich groundwater filled cavities and fractures in volcanic rock, later depositing microcrystalline quartz and iron oxides. Agate and jasper commonly formed in volcanic terrains from the Cenozoic or older geological periods.
Uses & applications
Used for cabochons, beads, carvings, bookends, and decorative tumbled stones; jasper is also used as an ornamental dimension stone.
Geological facts
Agate is typically translucent with banding or mossy inclusions, whereas jasper is more opaque and richly colored by iron and other impurities. Tumble-polishing enhances their waxy color and luster.
Field identification & locations
Look for quartz-like hardness, conchoidal fracture, waxy surfaces, and fine, non-granular texture; a steel knife should not scratch them. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.
