mineral

Polished dendritic agate / chalcedony

Microcrystalline quartz (SiO₂), likely agate with iron- or manganese-oxide inclusions

AI-generated identification · may be incorrect

Gray-black, cream, and translucent white banded chalcedony with a waxy to glassy luster; hardness about 6.5–7 Mohs, cryptocrystalline structure, no cleavage, and specific gravity near 2.6. The dark matrix and pale cavity suggest a polished or naturally weathered agate fragment.

Identified August 29, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills vesicles and fractures in volcanic rocks, depositing chalcedony in layers; iron or manganese oxides create dark dendritic patterns. Formation ages vary widely, commonly from Cenozoic to older volcanic sequences.

Uses & applications

Used for cabochons, beads, carvings, and small decorative specimens; ordinary pieces have modest lapidary value.

Geological facts

Agate’s fine banding and dendrites are often best revealed by polishing or slicing; its patterns are mineral inclusions rather than plant fossils.

Field identification & locations

Common in volcanic terrains worldwide, including Brazil, Uruguay, Mexico, India, Madagascar, and the western United States. It can be identified by its translucency, waxy surface, conchoidal fracture, and resistance to scratching by steel.