mineral
Chalcedony (possibly lavender or gray agate)
Microcrystalline quartz, SiO₂; fibrous quartz aggregate
AI-generated identification · may be incorrectTypically Mohs hardness 6.5–7, waxy to vitreous luster, translucent gray-lavender color, and conchoidal fracture with no cleavage. The cloudy, botryoidal texture and subtle concentric zoning are consistent with chalcedony, though the photograph cannot confirm the identification.
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Physical properties
Typically Mohs hardness 6.5–7, waxy to vitreous luster, translucent gray-lavender color, and conchoidal fracture with no cleavage. The cloudy, botryoidal texture and subtle concentric zoning are consistent with chalcedony, though the photograph cannot confirm the identification.
Formation & geological history
Forms when silica-rich groundwater precipitates in cavities, fractures, or volcanic vesicles, commonly replacing or lining host rock. It can form from Paleogene to Recent deposits, depending on locality.
Uses & applications
Used as ornamental stone, cabochons, carvings, beads, and lapidary material; durable varieties are also used for small tools and decorative objects.
Geological facts
Chalcedony is a cryptocrystalline quartz variety composed of microscopic quartz fibers. Lavender coloration may result from trace iron, manganese, or inclusions, while brown areas may be iron oxides or host-rock material.
Field identification & locations
Identify it by its waxy surface, hardness, translucency, and conchoidal fracture; it should scratch glass but not be scratched by a steel knife. Common sources include Brazil, Uruguay, India, Madagascar, Turkey, and the western United States.
