mineral

Chalcedony (Agate/Carnelian)

Cryptocrystalline Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: typically translucent grey, white, or blue (blue chalcedony); Luster: Waxy to Vitreous; Crystal Structure: Trigonal (microscopic); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.58–2.64

Hardness: 6
Color: typically translucent grey, white, or blue (blue chalcedony)
Luster: Waxy to Vitreous

Identified March 26, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater in volcanic rock cavities or sedimentary environments. It develops at relatively low temperatures as a precipitate from silica-rich fluids.

Uses & applications

Used primarily in jewelry (beads, cabochons), lapidary art, and ornamental carvings. Historically used for making stone tools and seals due to its toughness and fracture pattern.

Geological facts

Chalcedony is a cryptocrystalline form of quartz, meaning its crystals are too small to be seen without a microscope. The term 'agate' is used specifically when the chalcedony is banded, while 'chalcedony' usually refers to the translucent, un-banded variety.

Field identification & locations

Identify in the field by its waxy luster, translucency (hold to light), and smooth, curved (conchoidal) fracture surfaces. Commonly found in gravel pits, riverbeds, or as nodules in basalt and limestone. Collect in areas known for volcanic activity or ancient seabed deposits.

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