Alexandria is a sedimentary stone that is formed in hot springs and is composed of calcite calcium carbonate. All travertine stones will have natural cavities, or pits, visible in the stone that developed when carbon dioxide bubbles became trapped during the formation of the stone. As an unfilled travertine, the pits will remain visible and unfilled until they are filled with grout during installation. As a natural stone product, it is recommended that this be sealed to extend its longevity. Due to the nature of the tumbled finish, a stone-enhancing sealer will help to accentuate the natural colors in the stone that may be subdued after going through the tumbling process.