mineral

Chalcedony (Quartz variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Milky white to bluish-grey; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline (Trigonal/Monoclinic); Cleavage: None; Specific Gravity: 2.58–2.64.

Hardness: 6
Color: Milky white to bluish-grey
Luster: Waxy to vitreous

Identified April 22, 2026More mineral →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Milky white to bluish-grey; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline (Trigonal/Monoclinic); Cleavage: None; Specific Gravity: 2.58–2.64.

Formation & geological history

Formed from the deposition of silica-rich water in volcanic cavities (vesicles), sedimentary rocks, and hydrothermal veins. It typically forms at relatively low temperatures.

Uses & applications

Used in jewelry (cabochons and beads), ornamental carvings, hardstone carving, and historically for tools like arrowheads and seals.

Geological facts

Chalcedony has been used since the Bronze Age; the Romans used it for signet rings because wax wouldn't stick to the stone. It is the broad term for several varieties including agate and carnelian.

Field identification & locations

Identify by its waxy luster, conchoidal fracture (curved glass-like breaks), and lack of visible crystals. Commonly found in Brazil, India, Madagascar, and the USA (Pacific Northwest).