mineral

Banded Agate (specifically Sardonyx Agate)

Silicon Dioxide (SiO2) - Chalcedony variety

Hardness: 6.5–7 (Mohs scale); Color: Banded layers of white, grey, and reddish-brown (sard); Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.58–2.64

Hardness: 6
Color: Banded layers of white, grey, and reddish-brown (sard)
Luster: Waxy to vitreous

Identified March 9, 2026More mineral →

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Physical properties

Formation & geological history

Formed primarily in volcanic rock cavities (vesicles) where silica-rich groundwater deposits layers of chalcedony over thousands of years. This specimen shows classic rhythmic crystallization.

Uses & applications

Commonly used in jewelry (pendants, cameos, beads), lapidary art, and as ornamental healing stones. Historically used for making signet rings and hardstone carvings.

Geological facts

Agate was named by Theophrastus, a Greek philosopher, who discovered the stone along the shoreline of the Achates River in Sicily. It is a stone associated with protection and stability in many cultures.

Field identification & locations

Identify in the field by its distinct colorful banding and waxy texture when broken. It is often found in riverbeds or areas with ancient volcanic activity like Brazil, India, and the Lake Superior region of the USA.

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