Calcium carbide is a chemical compound with the chemical formula of CaC2. Its main use industrially is in the production of acetylene and calcium cyanamide.
The pure material is colorless, however pieces of technical-grade calcium carbide are grey or brown and consist of only 80-85% of CaC2 (the rest is CaO (calcium oxide), Ca3P2 (calcium phosphide), CaS (calcium sulfide), Ca3N2 (calcium nitride), SiC (silicon carbide), etc.). Because of presence of PH3 (phosphine), NH3 (ammonia), and H2S (hydrogen sulfide), technical-grade calcium carbide has a distinctive smell which some find unpleasant.
Read more about Calcium Carbide: Production, Crystal Structure