mineral
Tumbled carnelian/chalcedony
Chalcedony (microcrystalline quartz), SiO₂; reddish color from iron oxides
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; translucent gray-brown to red-orange, with a waxy to vitreous luster and no visible cleavage. It has a cryptocrystalline quartz structure and conchoidal fracture; the smooth surface indicates tumbling or water wear.
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Physical properties
Hardness 6.5–7 Mohs; translucent gray-brown to red-orange, with a waxy to vitreous luster and no visible cleavage. It has a cryptocrystalline quartz structure and conchoidal fracture; the smooth surface indicates tumbling or water wear.
Formation & geological history
Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, with iron staining producing red tones. Deposits commonly formed during the Cenozoic and older volcanic episodes.
Uses & applications
Used as an ornamental stone, beads, cabochons, carvings, and lapidary material; durable enough for minor decorative and historical tool uses.
Geological facts
Carnelian is the orange-red variety of chalcedony, while gray or brown translucent portions may be ordinary chalcedony. Heating can intensify its red color by oxidizing iron.
Field identification & locations
Identify by its waxy appearance, translucency, quartz hardness, and lack of cleavage; it should scratch glass but not be scratched by a steel knife. Common sources include India, Brazil, Uruguay, Madagascar, and the western United States.
