Margaritasite is a yellow, caesium-bearing mineral in the carnotite group. Its chemical formula is (Cs, K, H<sub>3</sub>O)<sub>2</sub>(UO<sub>2</sub>)<sub>2</sub>V<sub>2</sub>O<sub>8</sub>·H<sub>2</sub>O and its crystal system is monoclinic (space group P2<sub>1</sub>/a