High Quality Content by WIKIPEDIA articles! Todorokite is a rare complex hydrous manganese oxide mineral with formula (Mn,Mg,Ca,Ba,K,Na)2Mn3O12·3H2O. It is a brown to black monoclinic mineral which occurs in massive or tuberose forms. It is quite soft with a Mohs hardness of 1.5, and has a specific gravity of 3.49 - 3.82.