1. Rock composed of sand grains and/or sand-sized shell fragments cemented by calcium carbonate, commonly formed very rapidly on some beaches in tropical and sub-tropical areas. Beachrock generally occurs as thin beds between bedding planes that dip seawards at angles similar to those of the beach slope . 2. A friable to indurated rock consisting of sand grains of various minerals cemented by calcium carbonate; occurs in thin beds dipping seaward at less than 15N. Also known as beach sandstone .