mineral

Polished agate with black chalcedony inclusion

Banded chalcedony (microcrystalline quartz, SiO₂), likely agate or onyx-type material

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; brown, honey, and black coloration; waxy to vitreous luster; cryptocrystalline quartz with no visible cleavage and conchoidal fracture. The smooth surface indicates polishing or tumbling.

Identified September 12, 2026More mineral →

Explore Polished agate with black chalcedony inclusion in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing chalcedony and iron-stained bands over time, commonly during the Cenozoic or older volcanic episodes. The black area may be dense chalcedony, iron/manganese staining, or another included mineral.

Uses & applications

Used for cabochons, beads, carvings, ornaments, and small display specimens; durable polished agate is also used in decorative objects and lapidary work.

Geological facts

Agate colors commonly result from iron, manganese, and other trace elements. Exact identification of the dark inclusion requires testing or examination of an unpolished surface.

Field identification & locations

Identify by its glassy-to-waxy polish, hardness, conchoidal fracture, and fine color zoning; it should not scratch easily with a steel knife. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the United States.