Silicon nitride is a chemical compound of the elements silicon and nitrogen, with the formula . It is a white, high-melting-point solid that is relatively chemically inert, being attacked by dilute HF and hot . It is very hard (8.5 on the mohs scale). It is the most thermodynamically stable of the silicon nitrides. Hence, is the most commercially important of the silicon nitrides and is generally understood as what is being referred to where the term "silicon nitride" is used.