Chalcedony (Grey/White Agate)

Physical Properties

Hardness: 6.5-7 (Mohs scale); Color: Translucent grey to white with a brownish inclusion; Luster: Waxy to vitreous; Crystal Structure: Trigonal (cryptocrystalline); Cleavage: None; Specific Gravity: 2.58–2.64

Formation & Geological History

Formed from the deposition of silica from groundwater in cavities of igneous rocks such as basalt, or as a replacement mineral in sedimentary environments. Can be millions of years old based on the host rock formation.

Uses & Applications

Used primarily for jewelry (cabochons, beads), decorative carvings, and as a semi-precious collector's stone. Also used historically for tools and seals.

Geological Facts

Agate and Chalcedony are cryptocrystalline varieties of quartz, meaning their crystals are so small they can only be seen under extreme magnification. The term 'agate' is typically used when the specimen shows banding or color variations like the one seen here.

Field Identification & Locations

Identify by its waxy luster, translucency when held to light, and hardness (it will scratch glass). Commonly found in riverbeds, volcanic ash deposits, and desert regions globally.

Identified on: 4/24/2026

Mode: Standard