Agate

Agate is a banded variety of chalcedony, a fine-grained form of silica. It often shows contrasting colour bands and is used as a decorative stone, jewellery material, or collector’s specimen. Pattern, colour, and translucency vary from one specimen to another.

The name “agate” describes a geological stone type; it does not by itself establish the geographic origin, any treatment, or the market value of a particular piece. Such claims require separate documentation and assessment.

Source: British Geological Survey, Rock Classification Scheme: Agate.