Achat-Quarz agaat agat agata agate agate ahat ágata ágata αχάτης אגט נופך Cryptocrystalline chalcedony, showing a variegated banded structure and waxy luster. Agate bands are caused by the deposition of successive mineral layers from solution and may be either straight, wavy, or concentric. Agate is slightly harder than quartz. It has been gathered or mined since Neolithic times. It may distinguished from onyx by the parallel structure of the bars in onyx (AAT).