mineral
Tumbled brown chalcedony (likely agate)
Microcrystalline quartz, SiO₂; agate is banded chalcedony
AI-generated identification · may be incorrectTranslucent to opaque brown with a wet-looking vitreous luster; quartz crystal structure, no visible cleavage, Mohs hardness 6.5–7, specific gravity about 2.6. The image shows a rounded, polished pebble; banding is not clearly visible.
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Physical properties
Translucent to opaque brown with a wet-looking vitreous luster; quartz crystal structure, no visible cleavage, Mohs hardness 6.5–7, specific gravity about 2.6. The image shows a rounded, polished pebble; banding is not clearly visible.
Formation & geological history
Silica-rich fluids deposited quartz in cavities and fractures, commonly in volcanic rocks; agate formation spans many geological ages. Tumbling and polishing are human processing.
Uses & applications
Used for jewelry, ornaments, and lapidary collections; chalcedony is also used for carvings and small decorative objects.
Geological facts
Agate is a variety of chalcedony, and its defining bands may be subtle or absent in specimens sold as generic chalcedony.
Field identification & locations
Check for translucence, hardness, and conchoidal fracture; agates commonly occur in volcanic regions and river gravels worldwide. The photograph alone cannot confirm agate banding.
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