Boron nitride is a heat- and chemically resistant refractory compound of
boron and
nitrogen with the
chemical formula BN. It exists in various
crystalline forms that are
isoelectronic to a similarly structured
carbon lattice. The
hexagonal form corresponding to
graphite is the most stable and soft among BN polymorphs, and is therefore used as a lubricant and an additive to cosmetic products. The cubic (sphalerite structure) variety analogous to
diamond is called c-BN; it is softer than diamond, but its thermal and chemical stability is superior. The rare
wurtzite BN modification is similar to
lonsdaleite and may even be harder than the cubic form.