Cryptomelane
Cryptomelane is a potassium manganese oxide mineral with formula K(Mn,Mn)8O16.
In 1942 the name cryptomelane was proposed as part of an effort to sort out the manganese oxide minerals referred to as psilomelane. Cryptomelane was identified and defined based on X-ray diffraction studies of samples from Tombstone, Arizona; Deming, New Mexico; Mena, Arkansas; and Philipsburg, Montana.