Calcium silicate (often referred to by its shortened trade name Cal-Sil or Calsil) is the chemical compound Ca2SiO4, also known as calcium orthosilicate and sometimes formulated 2CaO.SiO2. It is one of a group of compounds obtained by reacting calcium oxide and silica in various ratios[4] e.g. 3CaO•SiO2, Ca3SiO5; 2CaO•SiO2, Ca2SiO4; 3CaO•2SiO2, Ca3Si2O7 and CaO•SiO2, CaSiO3. Calcium silicate is a white free-flowing powder derived from limestone and diatomaceous earth. It has a low bulk density and high physical water absorption. It is used in roads, insulation, bricks, roof tiles, table salt[5] and occurs in cements, where it is known as belite (or in cement chemist notation C2S).
It is used as an anti-caking agent in food preparation and an antacid. It is approved by the United Nations' FAO and WHO bodies as a safe food additive in a large variety of products.