Board material is a term used to describe the material used to make boards, such as those used in construction or for furniture. Two common board materials are EMERY and SLATE. EMERY is a hard, granular mineral composed of corundum, magnetite, and other minerals. It is often used as an abrasive material for grinding and polishing. SLATE is a fine-grained metamorphic rock composed of clay minerals and quartz. It is often used as a roofing material and for flooring, as well as for making chalkboards and other boards.