Chalcedony (Agate)

Physical Properties

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

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.

Identified on: 4/20/2026

Mode: Standard