Shigaite

Shigaite consists of oxycation sheets of [AlMn2(OH)6] intercalated with oxyanion sheets of [Na(H2O)6{H2O}6(SO4)2]. Linkage between the sheets and within the oxyanion sheet results largely through hydrogen bonding.

Shigaite was discovered in 1985 in the Ioi Mine, Shiga Prefecture, Japan. The original study, published in the journal Neues Jahrbuch für Mineralogie, Monatshefte, identified the formula as Al4Mn7(SO4)2(OH)22·8H2O. The formula was significantly revised in 1996 using a sample from the N'Chwaning Mine, South Africa. Sodium, discovered to be a component of shigaite, was not identified in the original study. However, an unidentified volatile had been noted that presumably was a sodium-containing complex.

As of 2012, shigaite is known from the following sites: Iron Monarch open cut, South Australia, Australia Poudrette quarry, Quebec, Canada Ioi mine, Shiga Prefecture, Japan Wessels Mine, Northern Cape Province, South Africa N'Chwaning Mine, Northern Cape Province, South Africa Homer Mine, Michigan, United States Bengal Mine, Michigan, United States The type material is housed in the National Museum of Natural History in Washington, D.C. as sample 122089.