The visible quartz crystals in this polished cabochon make it wonderfully distinctive. The deep red colour is likely to be from oxidised iron.
Agate is composed primarily of silicon dioxide. It has been found on every continent sometimes in great abundance. Only a very small percentage is attractive enough to be used for cutting and polishing.
Some of the earliest agate known to have been used for decorative purposes was found amongst artefacts from the ancient city of Ur (modern day Iraq). Patterned stones particularly beads were found in the tomb of Queen Puabi (c. 2600 BC).