Todorokite
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Todorokite is a complex hydrous manganese oxide mineral with generic chemical formula 1-x6O12·3-4H2O. It was named in 1934 for the type locality, the Todoroki mine, Hokkaido, Japan. It belongs to the
Todorokite with manjioite and calcite from the Smartt Mine, Kuruman District, South Africa
Cryptomelane
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Cryptomelane is the potassium endmember of the hollandite group, a family of tectomanganates with a 2 × 2 tunnel structure.
Polyhedral representation of the 2 × 2 tunnel structure of cryptomelane. The black atoms represent K.