Calcium carbide is a chemical compound containing calcium and carbide, with a chemical formula of CaC2. Pure calcium carbide is colorless, but most of the material is produced industrially, and is somewhat impure, giving it a black or grayish-white color, depending on the quality. The main use for calcium carbide is in the production of the flammable gas acetylene. When any grade of calcium carbide comes into contact with water, a chemical reaction immediately begins, which yields two new compounds, one of which is acetylene, a very useful flammable gas. This is the principal modern use of calcium carbide. Countries such as China use large amounts of acetylene as an industrial fuel, mainly because it is cheaper to make and use domestically than to import petroleum for the same purpose. Oddly enough, acetylene can also be used to speed up the ripening of fruit, in the same way that ethylene is used.