mineral
Gray chalcedony (common agate/jasper fragment)
Microcrystalline quartz, SiO₂; likely chalcedony with weathered host-rock rind
AI-generated identification · may be incorrectTypically Mohs hardness 6.5–7, waxy to vitreous luster, gray to bluish-gray translucent body, and no visible cleavage. The conchoidal fracture and fine-grained, microcrystalline texture are characteristic of chalcedony; minor pores or inclusions may be present.
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Physical properties
Typically Mohs hardness 6.5–7, waxy to vitreous luster, gray to bluish-gray translucent body, and no visible cleavage. The conchoidal fracture and fine-grained, microcrystalline texture are characteristic of chalcedony; minor pores or inclusions may be present.
Formation & geological history
Forms when silica-rich groundwater fills cavities, fractures, or vesicles in volcanic rock and later precipitates as fibrous quartz. The specimen is likely a weathered Cenozoic or older volcanic-host occurrence, but age cannot be determined from the image.
Uses & applications
Used for cabochons, carvings, beads, ornamental stone, and lapidary pieces; massive material has limited industrial use compared with quartz sand.
Geological facts
Chalcedony is a quartz variety rather than a separate chemical mineral species. Gray material may grade into agate, jasper, or silicified rock depending on banding, translucency, and impurities.
Field identification & locations
Look for conchoidal fracture, waxy luster, translucency at thin edges, and hardness sufficient to scratch glass. Common in volcanic terrains worldwide, including Mexico, Brazil, India, Turkey, and the western United States.
