Akhtenskite

Akhtenskite is a manganese oxide mineral with the chemical formula of MnO₂ (or: ε-Mn⁴⁺O₂) that was named after the Akhtensk deposit in Russia, where it was first discovered and noted in 1979. 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, all in Russia.

Akhtenskite
General
Category	Oxide mineral
Formula (repeating unit)	MnO2
IMA symbol	Akh
Strunz classification	4.DB.15b
Crystal system	Hexagonal Dihexagonal dipyramidal class
Space group	Hexagonal H-M symbol: (6/m 2/m 2/m) Space group: P63/mmc
Unit cell	a = 2.84, c = 4.6 [Å]; Z = 1
Identification
Color	Light gray to black
Crystal habit	Flaky polycrystalline aggregates
Cleavage	Distinct on {001}
Streak	Black
Diaphaneity	Opaque
Specific gravity	4.78 (calculated)
Optical properties	Uniaxial
References

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 and 37% manganese.

Some minerals that are commonly associated with akhtenskite are: todorokite, pyrolusite, nsutite, goethite, and cryptomelane.