Sandstone is a sedimentary rock formed by the action of wind, water and ice on older rock. It is composed of sand-like crystals of quartz cemented together by silica, lime or iron oxide. Formed in or near ancient seas, sandstone may contain fossilized sea animals. It can be cut into blocks and used for building construction. Great for science projects or classroom collection. Each piece is irregularly shaped and is between 0.5 and 1 inch in size.