Segelerite is a complex phosphate mineral with formula CaMgFe³⁺OH(PO₄)₂·H₂O. It occurs in pegmatites and forms striking green or chartreuse crystals. It was discovered in 1974 in the Black Hills of South Dakota by an amateur mineralogist from New York, Curt G. Segeler (1901-1989), after whom it is named.