TEPHROITE

olivine mineral found only in iron-manganese ore deposits and skarns and in metamorphosed manganese-rich sediments, such as those of Cornwall, Eng., and Franklin, N.J., in the United States. Tephroite (manganese silicate; Mn2SiO4) forms a solid solution series with the olivine fayalite in which iron completely replaces manganese in the molecular structure. Minerals intermediate in composition to these are called knebelite. For detailed physical properties, see olivine (table).