mineral

Tumbled purple agate (likely grape agate or amethystine chalcedony)

Microcrystalline quartz, SiO₂; purple coloration commonly from iron, manganese, or inclusions

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent purple-gray with darker dendritic or brecciated patterns and a waxy-to-glassy luster. Quartz has trigonal crystal structure, but chalcedony is cryptocrystalline and lacks visible cleavage.

Identified August 7, 2026More mineral →

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At a glance

Common name: Tumbled purple agate (likely grape agate or amethystine chalcedony)
Scientific name: Microcrystalline quartz, SiO₂; purple coloration commonly from iron, manganese, or inclusions
Category: mineral
Identified: August 7, 2026
Method: Standard

AI Estimated Value

About $5–$25 for a small tumbled stone; $25–$100+ for unusually vivid, natural, patterned material.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing layered chalcedony and quartz over time; the specimen was later cut and polished. Most examples formed in Cenozoic volcanic terrains, though exact age is locality-dependent.

Uses & applications

Used for cabochons, beads, carvings, ornaments, and lapidary collections; durable but generally not high-value jewelry material.

Geological facts

“Grape agate” is a trade name for botryoidal purple chalcedony, especially from Indonesia; the pictured smooth stone may instead be dyed or naturally purple agate.

Field identification & locations

Identify by its glassy/waxy polish, fine internal banding or mossy patterns, absence of cleavage, and ability to scratch glass. Common sources include Indonesia, Brazil, Uruguay, Mexico, and Madagascar.