Romanèchite

Romanèchite ((Ba,H₂O)₂(Mn⁴⁺,Mn³⁺)₅O₁₀) is the primary constituent of psilomelane, which is a mixture of minerals. Most psilomelane is not pure romanechite, so it is incorrect to consider them synonyms. Romanèchite is a valuable ore of manganese, which is used in steelmaking and sodium battery production.^[6] It has a monoclinic crystal structure, a hardness of 6 and a specific gravity of 4.7–5. Romanèchite's structure consists of 2 × 3 tunnels formed by MnO₆ octahedra.^[5][7]

Romanèchite
Romanèchite, from the Marquette County, Michigan, US.
General
Category	Oxide minerals
Formula	(Ba,H2O)2(Mn4+,Mn3+)5O10
IMA symbol	Rmn[1]
Strunz classification	4.DK.10
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/m
Identification
Mohs scale hardness	6–6.5
Luster	Submetallic
Streak	Blue-black
References	[2][3][4]

Polyhedral representation of the 2 x 3 tunnel structure of romanèchite. The red atoms represent Ba and H₂O.^[5]

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.^[8] It occurs also in ferromanganese nodules from Lake Baikal.^[9]

• 
  Bicolor (left) and tricolor (right) X-ray fluorescence maps of the distribution of Mn, Fe, and Ba in a ferromanganese nodule from Lake Baikal. Size = 5 mm (H) × 3 mm (V).^[9]