Agates from Yozgat are showing colours only very rarely - however they are because of their complicated internal structure desired items of collection.
A multiplicity of valves (influxopenings) testifies the expansion of the semidurable gel during the silicate-agglomeration-process.
Also the formation of fascinating “shadow-effect-agates” distinguishes the agates of Yozgat.
Beside agate-nodules originating from basaltic host-rock also thundereggs in acidous vulcanites do occur. They are showing brown to black shades in their banding.