Mineral

Chalcedony

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 (Mohs); Color: Waxy grey-white, pale blue, or translucent yellow; Luster: Waxy to vitreous; Crystal Structure: Hexagonal (Trigonal, cryptocrystalline); Cleavage: None; Specific Gravity: 2.58–2.64.

Hardness: 6
Color: Waxy grey-white, pale blue, or translucent yellow
Luster: Waxy to vitreous

Identified March 2, 2026More mineral →

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Physical properties

Formation & geological history

Forms primarily in volcanic and sedimentary environments through the deposition of silica from water. It often fills cavities (amygdules) in igneous rocks or as nodules in limestone. Geological age varies from Cenozoic to Precambrian.

Uses & applications

Used extensively in jewelry for cabochons and beads, as an ornamental stone for carvings, and historically for stone tools due to its conchoidal fracture. Also used in precision bearings and grindstones.

Geological facts

Chalcedony is a broad term that includes varieties like agate, jasper, and carnelian. It was named after the ancient Greek town Chalcedon in Asia Minor. It is known for its extreme toughness compared to pure crystalline quartz.

Field identification & locations

Identify in the field by its waxy luster, smooth conchoidal fracture, and translucency on thin edges. Commonly found in Brazil, India, Madagascar, and the Western United States. Collectors should look for unique banding or botryoidal (grape-like) habits.