mineral
Tumbled gray-blue agate/chalcedony
Microcrystalline quartz (SiO₂), likely banded chalcedony or agate
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; translucent gray-blue body with subtle pale banding, vitreous/waxy luster, and no visible cleavage. Dense, fine-grained cryptocrystalline quartz; apparent brown edge may be lighting or iron staining.
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Physical properties
Hardness about 6.5–7 Mohs; translucent gray-blue body with subtle pale banding, vitreous/waxy luster, and no visible cleavage. Dense, fine-grained cryptocrystalline quartz; apparent brown edge may be lighting or iron staining.
Formation & geological history
Forms when silica-rich groundwater fills cavities in volcanic rock, depositing chalcedony and quartz in layers over geologic time, commonly from the Cenozoic to Paleozoic. The specimen has been cut and polished into a tumbled stone.
Uses & applications
Used for lapidary ornaments, cabochons, beads, carvings, and decorative objects; usually modestly valued as a polished collectible.
Geological facts
Agate is technically a banded variety of chalcedony, while visually similar unbanded material is generally called chalcedony. Its color can be natural or enhanced by dyeing or heat treatment.
Field identification & locations
Identify by its waxy-to-glassy luster, translucency, curved fracture, lack of cleavage, and resistance to scratching by ordinary steel. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.
