Nodular mass of black todorokite, intergrown with romanechite, birnessite, and other manganese minerals. From Calvert Cliffs, Calvert County, Maryland. Specimen is about 4 cm high. (Photo by W. Cordua.)
Formula: (Ca,K,Na,Mg,Ba,Mn)(Mn,Mg,Al)6O12.3H2O Monoclinic
Description: Todorokite is soft sooty brown, gray to black mineral formed as a result of the alteration of other manganese minerals or as a precipitate from surficial waters.
Todorokite is reported as a component of the small manganese nodules found at various sites in Lake Michigan, particularly in Green Bay (Rossman et al., 1972).
Properties of minerals 