Shelf material can refer to a variety of materials used to construct shelves, such as wood, metal, or plastic. Two natural materials that can be used for shelf construction are shale and ICE. Shale is a type of sedimentary rock composed of clay minerals and other small particles. It is formed by the compaction of mud and silt over time. ICE is a solid form of water, which can be found naturally in glaciers, snow, and frozen bodies of water.