Formed over 50 million years ago, Agate is one of the hardest and most beautiful of all minerals. The patterns and designs you see are solely at the whim of nature, the color has been enhanced. Occasionally, cavities lined with quartz crystals are present. Bookends are sold by the pair, these are the pair you are buying. They are 8 1/2″w X 4 1/2″ h.