mineral
Tumbled agate or chalcedony
Microcrystalline quartz (SiO₂), likely iron-stained chalcedony/agate
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; brown, gray, reddish-brown, and black coloration; waxy to vitreous luster; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The smooth rounded surface indicates tumbling or water wear.
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Physical properties
Hardness about 6.5–7 Mohs; brown, gray, reddish-brown, and black coloration; waxy to vitreous luster; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The smooth rounded surface indicates tumbling or water wear.
Formation & geological history
Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, often developing iron-oxide colors and subtle banding; commonly Paleozoic to Cenozoic, depending on locality. Exact origin cannot be determined from the photograph.
Uses & applications
Used as a lapidary stone for cabochons, beads, carvings, and ornamental objects; attractive pieces are collected as polished specimens.
Geological facts
Agate is a variety of chalcedony distinguished by cryptocrystalline quartz and commonly banded or mossy internal patterns. This specimen may also be jasper-rich chalcedony if it is opaque throughout.
Field identification & locations
Commonly found in volcanic regions, especially Brazil, Uruguay, Mexico, India, Madagascar, and the western United States. A translucent edge, curved banding, glass-scratch hardness, and lack of fizz in dilute acid support identification; photograph-only identification is approximate.
