Romanèchite ((Ba,H2O)2(Mn4+,Mn3+)5O10) is the primary constituent of psilomelane, which is a mixture of minerals.

Romanèchite is a valuable ore of manganese, which is used in steelmaking and sodium battery production.

Romanèchite's structure consists of 2 × 3 tunnels formed by MnO6 octahedra.

[5][7] It is commonly associated with hematite, barite, pyrolusite, quartz and other manganese oxide minerals.

It has been found in France, Germany, England, Brazil, Russia, India, and various parts of the United States, including Arizona, Virginia, Tennessee and Michigan, and sites throughout the Appalachian Valley and Ridge.