mineral

Chalcedony (Agate)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Pale orange to cream translucent; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline (Trigonal/Monoclinic); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.58–2.64

Hardness: 6
Color: Pale orange to cream translucent
Luster: Waxy to vitreous

Identified April 20, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica-rich groundwater in cavities of igneous rocks or sedimentary layers. This specimen shows water-worn tumbling and iron staining, likely found in a riverbed or coastal environment.

Uses & applications

Used widely in lapidary work for making cabochons, beads, and jewelry. It is also a popular specimen for rock tumbling and collector display.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen with a microscope. The 'pockmarked' texture on this specimen suggests it may have once been part of a geode or had softer inclusions that weathered away.

Field identification & locations

Identify in the field by its translucency (waxy 'glow' when backlit), lack of visible crystals, and extreme hardness (will scratch glass). Commonly found in gravel beds and volcanic regions.