Akhtenskite is a manganese with the chemical formula of MnO2 (or: ε-Mn4+O2 ) that was named after the Akhtensk deposit in Russia It can be found in the Akhtensk brown ironstone deposit, in the southern Ural Mountains , on Mt. Zarod, on the Sikhote-Alin Mountains , and in the Primorskiy Krai
Its crystals are usually hexagonal in shape, with flakiness and plating, usually because it replaced a mineral. Akhtenskite is a polymorphous with the much more widespread pyrolusite. It occurs in mixtures with "psilomelane" (recently renamed to romanechite) and with other manganese oxides in an iron oxide deposit, most likely bacterially altered from a previous mineral in the Akhtensk deposit. It also occurs in crusts of ferromanganese minerals on oceanic rocks. Its chemical makeup is 63% oxygen.
Some minerals that are commonly associated with akhtenskite are: todorokite, goethite