Cryptomelane (K(Mn4+,Mn2+)8O16) is the potassium endmember of the hollandite group, a family of tectomanganates with a 2 × 2 tunnel structure.

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.

[2][3] It is of rather common occurrence in oxidized manganese deposits where it occurs as replacements and open space fillings in veins and vugs.

It occurs in association with hollandite, pyrolusite, nsutite, braunite, chalcophanite, manganite and various other manganese oxides.