mineral

Tumbled purple chalcedony (likely grape agate)

Chalcedony, cryptocrystalline quartz (SiO₂), with purple manganese-bearing inclusions

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; lavender-purple color, waxy to vitreous luster, translucent edges, and no visible cleavage. The rounded, polished surface and botryoidal-looking pattern are typical of grape agate/chalcedony.

Identified September 3, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures in volcanic rock, depositing microscopic quartz and moganite; purple color commonly reflects manganese. Not assigned a single age; specimens are especially associated with Miocene volcanic regions of Mamuju, West Sulawesi, Indonesia.

Uses & applications

Used as a lapidary stone, cabochon, ornamental object, and mineral-collection specimen; durable but generally less valuable than fine amethyst or high-grade agate.

Geological facts

Grape agate is a trade name for botryoidal purple chalcedony, not a separate mineral species. Strong color, distinct grape-like globules, translucency, and natural patterning increase desirability.

Field identification & locations

Identify by testing scratch resistance against steel or glass, examining waxy luster and conchoidal fracture, and checking for dyed color in cracks or surface pits. Common sources include Indonesia, Brazil, Uruguay, and Mexico.