Agate (Moss or Plume Agate variety)

Physical Properties

Hardness: 6.5-7 (Mohs scale). Color: White, translucent centers with brown, orange, and green inclusions. Luster: Vitreous to waxy. Crystal Structure: Hexagonal (cryptocrystalline). Cleavage: None, conchoidal fracture.

Formation & Geological History

Formed through the deposition of silica from groundwater in the cavities of igneous rocks, particularly volcanic lavas. Most are deposited in layers or dendritic patterns over thousands of years.

Uses & Applications

Used primarily in lapidary arts, jewelry (cabochons), interior decoration, and as a collector's specimen. Historically used for making mortars and pestles because of its hardness.

Geological Facts

Agates are found inside geodes or as nodules in volcanic rock. The unique colors are often caused by trace amounts of iron, manganese, or nickel. Many specimens from the American West date back to the Eocene epoch.

Field Identification & Locations

Identify in the field by its waxy texture and translucent 'window' when held to light. It lacks the graininess of sandstone and is hard enough to scratch glass. Commonly found in riverbeds or desert regions of the Western US.

Identified on: 5/11/2026

Mode: Standard