Agate (Chert/Chalcedony)

Physical Properties

Hardness: 6.5–7 on Mohs scale; Color: Brown, tan, and translucent white/grey; Luster: Waxy to vitreous; Crystal Structure: Trigonal (Microcrystalline); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6

Formation & Geological History

Formed as a secondary mineral in volcanic or sedimentary rocks through the deposition of silica from groundwater into cavities or fractures. This specific specimen appears to be a stream-tumbled water-worn nodule.

Uses & Applications

Used primarily in lapidary arts for jewelry, ornaments, and as semi-precious gemstones. Historically used for making stone tools due to its hardness and sharp fracture edges.

Geological Facts

Agates often feature concentric banding, though this specimen shows 'cloud' or 'moss' like inclusions. They are known for their durability and was used by ancient civilizations for amulets and seals.

Field Identification & Locations

Identify in the field by its waxy texture, translucent edges when held to light, and lack of visible grains. Common in gravel pits, riverbeds, and volcanic outcrops globally.

Identified on: 4/16/2026

Mode: Standard