English Walnut is a very dense travertine, quarried 8,000 feet above sea level near the Andes Mountains in Peru. This sedimentary stone was formed in hot springs and is composed mainly of calcite calcium carbonate. All travertines will have natural cavities, or pits, visible in the stone. These cavities were developed when carbon dioxide bubbles became trapped during the formation of the stone. Prior to honing, English Walnut is filled with a colored cement to fill in these cavities. During the summer months the cement will dry more quickly then it will during the more humid portions of the year. Because of the fluctuation in curing, it is normal for the tone of the fill to differ between seasons. There can be noticeable variances between pieces, so it is important and recommended that a range of this product be viewed before finalizing a purchase. As a natural stone product, it is recommended that this be sealed to extend its longevity.