Imported Calcium Carbonate can be used to make pure calcium carbonate, or it can be made by adding carbon dioxide to a calcium hydroxide solution. It functions as an antacid, a food colouring, a food firming agent, and a fertilizer, among other things. It's a one-carbon molecule, a calcium salt, and a carbonate salt. Calcium Carbonate is a colourless powder or crystal that is white and odourless. Water-insoluble to a large extent. It's found in a lot of rocks all around the planet.