Mesaite is a very rare mineral with formula CaMn<sup>2+</sup><sub>5</sub>(V<sub>2</sub>O<sub>7</sub>)<sub>3</sub>â¢12H<sub>2</sub>O. It is monoclinic (space group P2/n). It is related to fianelite, another manganese-rich divanadate. Examples of other divanadate minerals are volborthite, engelhauptite, karpenkoite, and martyite.