Bosphorus Limestone is a cool gray limestone. Bosphorus Limestone blocks are medium to small and it can yield size up to 12x24 with a consistent background. We recommend limestone tiles, limestone mosaics and limestone moldings.Per Wikipedia, Limestone is a sedimentary rock, composed mainly of skeletal fragments of marine organisms such as coral and mollusks. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3).About 10% of sedimentary rocks are limestones. The solubility of limestone in water and weak acid solutions leads to karst landscapes, in which water erodes the limestone over thousands to millions of years. Most cave systems are through limestone bedrock.