Hydroxyapatite is a calcium phosphate mineral that makes up about 70% of the inorganic component of bone and teeth in humans and other animals. It has the chemical formula Ca10(PO4)6(OH)2. Hydroxyapatite is a naturally occurring mineral form of calcium apatite, with the idealized crystal structure consisting of alternating calcium and phosphate layers.

In addition to its natural occurrence in bone and teeth, hydroxyapatite has various medical applications due to its biocompatibility and osteoconductive properties. It is used as a coating on orthopedic implants to promote bone growth and integration with the implant, and it is also used in dental and oral healthcare products for remineralization of tooth enamel. Furthermore, hydroxyapatite has been studied for its potential use in drug delivery systems, tissue engineering, and other biomedical applications.