Natural marine microcrystalline hydroxyapatite (MCHA) is a form of hydroxyapatite derived from the bones of marine fish, such as sustainably harvested fish like salmon and haddock. Hydroxyapatite is a mineral compound primarily composed of calcium and phosphorus, and it closely resembles the mineral composition of human bone. Natural MCHA is often used as a dietary supplement due to its potential benefits for bone health and calcium supplementation.