Limestone is a sedimentary rock, composed maly of skeletal fragments of mare organisms such as coral, forams and molluscs. Its major materials are the merals calcite and aragonite, which are different crystal forms of calcium carbonate. About 10% of sedimentary rocks are limestones. The solubility of limestone water and weak acid solutions leads to karst landscapes, which water erodes the limestone over thousands to millions of years. Most cave systems are through limestone bedrock.