mineral
Tumbled chalcedony (likely agate or jasper)
Microcrystalline quartz, SiO₂ (chalcedony)
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; cream to tan, waxy-to-dull luster, cryptocrystalline structure, no visible cleavage, and conchoidal fracture. The rounded shape and polish indicate a tumbled specimen; brown markings may be iron oxides or included host material.
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Physical properties
Hardness 6.5–7 Mohs; cream to tan, waxy-to-dull luster, cryptocrystalline structure, no visible cleavage, and conchoidal fracture. The rounded shape and polish indicate a tumbled specimen; brown markings may be iron oxides or included host material.
Formation & geological history
Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, precipitating microscopic quartz over time; the exact geological age depends on its source deposit. Commonly associated with basaltic volcanic terrains and sedimentary silica deposits.
Uses & applications
Used for cabochons, beads, carvings, lapidary pieces, and decorative objects; lower-grade material is inexpensive and sold as a polished stone.
Geological facts
Chalcedony is a broad quartz variety that includes agate, jasper, onyx, and bloodstone. Precise identification of the subtype is difficult from this photograph alone.
Field identification & locations
Field clues include translucent edges, glassy or waxy appearance, very high scratch resistance, and lack of cleavage; it should not be scratched with a steel knife easily. Common sources include Brazil, Uruguay, India, Madagascar, and the western United States.
