Manganese also substitutes for (Fe,Mg) within cummingtonite amphibole, replacing B site atoms. These minerals are found in high-grade metamorphic banded iron formation and form a compositional series between Mn 2Mg 5Si 8O 22(OH) 2 (tirodite) and Mn 2Fe 5Si 8O 22(OH) 2 (dannemorite).