Formula: (Fe,Mn)(Ta,Nb)2O6 – (Mn,Fe)(Ta, Nb)2O6 Tetragonal
Description: A series exists between ferri-tapiolite and manganotapioltie. These rare minerals are found in complex granite pegmatites.
MARATHON COUNTY: A member of the tapiolite series is found as rare small black masses in pegmatites at the Koss Pit (SW sec. 2 T.27 N. R.5E.) SW of Rib Mountain. (Buchholz, Falster and Simmons, 1999, 2000)