mineral

Polished agate (likely moss or plume agate)

Microcrystalline quartz, primarily chalcedony (SiO₂), with possible iron-oxide inclusions

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent gray, cream, and brown zones with a waxy-to-glassy luster. Fibrous microcrystalline quartz commonly shows curved or plume-like banding and no visible cleavage; specific gravity is about 2.6.

Identified August 30, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rocks, depositing chalcedony in successive layers; inclusions create the brown patterns. The specimen’s exact geological age cannot be determined visually, but agates commonly form during cooling and alteration of volcanic rocks over millions of years.

Uses & applications

Used for cabochons, carvings, beads, polished slices, bookends, and decorative objects; generally inexpensive but attractive patterned pieces are collectible.

Geological facts

Agate is a variety of chalcedony, and its banding may record repeated changes in groundwater chemistry. Polishing enhances translucency and internal patterns.

Field identification & locations

Identify it by its waxy luster, translucency, curved internal zoning, and hardness sufficient to scratch ordinary glass. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.