mineral

Chalcedony (Agate)

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Variable, often translucent white or gray with iron-oxide staining; Luster: Waxy to vitreous; Crystal structure: Hexagonal (trigonal) cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.58-2.64.

Hardness: 6
Luster: Waxy to vitreous

Identified May 18, 2026More mineral →

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Physical properties

Formation & geological history

Formed by the deposition of silica from groundwater in cavities of igneous or sedimentary rocks. This specific specimen appears to be a water-worn river pebble where iron staining has occurred within internal fractures or on the surface.

Uses & applications

Used extensively in lapidary work for cabochons and beads, as well as industrial applications like mortars and pestles due to its hardness and resistance to chemicals.

Geological facts

Chalcedony is composed of microscopic fibers of quartz and moganite. Known as a 'nurturing stone' in some cultures, it has been used since the Bronze Age for seals and jewelry in the Mediterranean and Middle East.

Field identification & locations

Identify in the field by its translucency, conchoidal fracture, and inability to be scratched by a steel blade. Commonly found in riverbeds, gravel pits, and volcanic areas. Look for a waxy texture when wet.