A modulated 2:1 layer silicate with continuous Mn-rich octahedral sheets and 6-fold tetrahedral rings forming islands three rings wide. These islands have inter-island linkages, some of which have inverted tetrahedra, involving 12-fold tetrahedral rings and double four-member rings, which act to link adjacent tetrahedral sheets (Eggleton and Guggenheim, 1994). A structural formula for parsettensite is M_7.5(Mn,Mg)₄₉(Si_64.5Al_7.5)_Σ=72O₁₆₈(OH)₅₀ ^. nH₂O. Parsettensite occurs in (low grade to very low grade) metasedimentary manganese ore deposits in Val d’Err, Oberhalbstein, Graubünden, Switzerland and on surfaces of pegmatite minerals by either hydrothermal or pneumatalytic processes at the Foote mine, Kings Mountain, North Carolina, USA, and in a very low grade metagraywacke and argillite near Otago, New Zealand.
Cf., stilpnomelane