Manganotantalite: Gemstone Information
Manganotantalite is (Mn2,Fe2)(Ta,Nb)2O6 and forms short prismatic crystals of the orthorhombic system, some transparent and scarlet red.There is one direction of distinct cleavage and the hardness is 5.5–6.5.The SG is 7.7–7.9 and the RI for the alpha, beta and gamma rays is 2.14,2.15 and 2.22, biaxial positive with birefringence 0.150. Manganotantalite occurs in granite pegmatites. Most gem material has come from Salinas,Minas Gerais, Brazil and from Morrua, Mozambique. Large crystals have been found at Amelia, Virginia, USA, a major deposit for the manganese garnet, spessartine.