sedimentary

Chalcedony (Agate)

Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs), Color: Translucent yellowish-tan, Luster: Waxy to vitreous, Crystal Structure: Trigonal (microcrystalline), Cleavage: None, Conchoidal fracture

Hardness: 6

Identified July 13, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs), Color: Translucent yellowish-tan, Luster: Waxy to vitreous, Crystal Structure: Trigonal (microcrystalline), Cleavage: None, Conchoidal fracture

Formation & geological history

Formed via precipitation of silica-rich groundwater in cavities of igneous or sedimentary rocks. This specimen appears to be a river-worn or water-eroded nodule.

Uses & applications

Used for lapidary work, jewelry, decorative carvings, and as a semi-precious gemstone due to its durability.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen with a regular microscope. It has been used for making seal stones and jewelry since the Bronze Age.

Field identification & locations

Identify in the field by its translucency (light passes through edges), waxy texture when wet, and lack of visible crystal grains. Often found in gravel beds or volcanic regions.