mineral

Agate (Chalcedony)

Silicon Dioxide (SiO2)

Hardness 6.5-7 on Mohs scale; color ranges from pale yellow to translucent amber; waxy to vitreous luster; microcrystalline/cryptocrystalline trigonal structure; absent cleavage; conchoidal fracture.

Identified July 28, 2026More mineral →

Explore Agate (Chalcedony) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness 6.5-7 on Mohs scale; color ranges from pale yellow to translucent amber; waxy to vitreous luster; microcrystalline/cryptocrystalline trigonal structure; absent cleavage; conchoidal fracture.

Formation & geological history

Formed via low-temperature deposition of silica from groundwater inside gas cavities (vesicles) of volcanic and metamorphic rocks.

Uses & applications

Popular for gemstone lapidary work, tumbling, jewelry, and ornamental carvings. Historically used for making mortars, pestles, and precision bearings.

Geological facts

Chalcedony is composed of fine intergrowths of quartz and moganite. Translucent, smooth beach-worn or gravel-derived chalcedony nodules are frequently referred to as 'agate' or 'carnelian' depending on color intensity.

Field identification & locations

Identified by its waxy luster, hardness (scratches glass, unaffected by steel knife), translucent nature, and lack of crystal faces or cleavage. Commonly found along river gravels, beaches, and volcanic fields globally.