sedimentary
Chalcedony
Silicon Dioxide (SiO2)
Hardness of 6.5 to 7 on the Mohs scale, colors range from white to gray, blue, or brownish, waxy to vitreous luster, cryptocrystalline or microfibrous crystal structure, conchoidal fracture with no true cleavage, specific gravity of 2.58 to 2.62.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, colors range from white to gray, blue, or brownish, waxy to vitreous luster, cryptocrystalline or microfibrous crystal structure, conchoidal fracture with no true cleavage, specific gravity of 2.58 to 2.62.
Formation & geological history
Forms in low-temperature aqueous environments, typically by the deposition of silica from underground waters in cavities and fractures of rocks, often associated with volcanic environments.
Uses & applications
Used in ornamental carvings, jewelry making, lapidary arts, and as a semi-precious gemstone.
Geological facts
Chalcedony is the parent material for many other cryptocrystalline quartz varieties such as agate, jasper, and onyx. Ancient civilizations used it frequently for intaglios, seals, and signet rings.
Field identification & locations
Can be identified by its waxy luster, conchoidal fracture, translucency, and hardness that easily scratches glass. Found worldwide, with major deposits in Brazil, India, Madagascar, and the USA.
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