mineral
Tumbled carnelian/chalcedony
Orange chalcedony (microcrystalline quartz), SiO₂; possibly iron-stained agate
AI-generated identification · may be incorrectTypically Mohs hardness 6.5–7, waxy to vitreous luster, orange to reddish-orange color, translucent edges, and no visible cleavage. The specimen appears smoothly tumbled, with cloudy white-gray quartz patches and iron-oxide coloration.
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Physical properties
Typically Mohs hardness 6.5–7, waxy to vitreous luster, orange to reddish-orange color, translucent edges, and no visible cleavage. The specimen appears smoothly tumbled, with cloudy white-gray quartz patches and iron-oxide coloration.
Formation & geological history
Forms when silica-rich groundwater fills cavities and fractures, later developing cryptocrystalline quartz; orange color comes mainly from hematite or limonite. Chalcedony deposits occur from Precambrian to recent ages in volcanic and sedimentary environments.
Uses & applications
Used for beads, cabochons, carvings, and ornamental objects; durable pieces are popular inexpensive gemstones and lapidary material.
Geological facts
Carnelian is the orange-red variety of chalcedony, while sard is the darker brown-red variety; boundaries between them are gradual. Heating can intensify its orange-red color.
Field identification & locations
Identify by its hardness, smooth waxy appearance, translucency, and lack of cleavage; it should resist scratching by a steel knife but scratch glass. Common sources include India, Brazil, Uruguay, Madagascar, and the United States.
