Characteristically formed carnelians are occuring on the Coromandel peninsula. They are showing areas of wheathered opaque chalcedony that is usually bright colored, in the outer rim. Inside usually a translucent reddish-coloured area can be found. This originally grey coloured agates have gotten their reddish coloring by the inclusion of iron. Worldwide this process took place on several places - one further example is given by the carnelians from Madagascar.