mineral
Polished gray chalcedony (likely agate)
Microcrystalline quartz, SiO₂; chalcedony, possibly banded agate
AI-generated identification · may be incorrectMohs hardness 6.5–7; gray-brown, waxy to vitreous luster, cryptocrystalline quartz structure, no visible cleavage, and conchoidal fracture. The rounded form appears polished or tumbled; banding is not clear in the image.
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Physical properties
Mohs hardness 6.5–7; gray-brown, waxy to vitreous luster, cryptocrystalline quartz structure, no visible cleavage, and conchoidal fracture. The rounded form appears polished or tumbled; banding is not clear in the image.
Formation & geological history
Silica-rich groundwater deposits quartz in cavities and fractures, forming chalcedony, often over millions of years. The exact geological age and source cannot be determined from the photo.
Uses & applications
Commonly used for beads, cabochons, carvings, and decorative objects; also collected as a polished specimen.
Geological facts
Agate is a variety of chalcedony distinguished by visible or microscopic bands; not all gray chalcedony is agate.
Field identification & locations
Look for hardness, a waxy luster, and curved conchoidal breaks; banding can help identify agate. Chalcedony occurs worldwide, including Brazil, Uruguay, India, and the western United States.
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