mineral

Chalcedony

Silicon Dioxide (SiO2)

Hardness of 6.5 to 7 on the Mohs scale, waxy or vitreous luster, translucent to opaque, crypto-crystalline structure (microscopic quartz fibers), conchoidal fracture with no true cleavage, specific gravity of 2.58 to 2.64.

Identified August 4, 2026More mineral →

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Physical properties

Formation & geological history

Forms in low-temperature hydrothermal environments, cavities of volcanic rocks, and sedimentary environments where silica-rich groundwater deposits microcrystalline quartz over geological time.

Uses & applications

Used in gemstone carving, lapidary art, ornamental items, and jewelry.

Geological facts

Chalcedony is the mother mineral for many well-known varieties including agate, jasper, onyx, and carnelian. Ancient civilizations frequently used chalcedony for intricately carved seals and signet rings due to its durability and how cleanly it takes a polish.

Field identification & locations

Identified by its waxy luster, conchoidal fracture, and lack of visible crystal faces without a microscope. Common worldwide, particularly in volcanic regions and river gravels where weathered nodules accumulate.