sedimentary
Agate Nodule / Chalcedony
Silicon Dioxide (SiO2)
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture, variable colors including grey, white, brown, and tan.
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Physical properties
Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture, variable colors including grey, white, brown, and tan.
Formation & geological history
Formed through the deposition of silica from groundwater solutions in cavities of ancient volcanic or sedimentary rocks, often over millions of years.
Uses & applications
Used in ornamental carvings, jewelry, lapidary arts, and as mineral specimens for collectors.
Geological facts
Agate is a variety of chalcedony that often forms in concentric bands. The vesicular (pitted) outer cortex seen here is typical of weathering in volcanic host rocks like basalt.
Field identification & locations
Can be identified by its waxy luster, conchoidal fracture, and hardness which scratches glass. Found worldwide in regions with volcanic activity.
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