Nioboheftetjernite, ScNbO (sub 4) , a new mineral from the Befanamo pegmatite, Madagascar

A new mineral, nioboheftetjernite, ideally ScNbO (sub 4) , was found in the Befanamo pegmatite, Analamanga, Madagascar. It occurs as anhedral grains and very crude elongated crystals up to 200 mu m in length in an intergrowth with rossovskyite, ilmenite, rutile, thortveitite, euxenite-(Y), feldspar, and quartz. The mineral is black with dark-brown to black streak and submetallic luster. It has no cleavage and its fracture is uneven. D (sub calc) is 5.855 g/cm (super 3) . The Raman spectrum and reflectance data are reported. The chemical composition (wt.%) is MgO 0.06, MnO 2.49, Fe (sub 2) O (sub 3) 12.14, Sc (sub 2) O (sub 3) 11.34, TiO (sub 2) 5.94, SnO (sub 2) 1.45, Nb (sub 2) O (sub 5) 32.23, Ta (sub 2) O (sub 5) 29.93, WO (sub 3) 3.38, total 98.96. The empirical formula calculated on the basis of 4 O apfu is (Sc (sub 0.40) Fe (super 3+) (sub 0.37) Ti (sub 0.15) Mn (super 2+) (sub 0.08) ) (sub Sigma 1.00) (Nb (sub 0.58) Ta (sub 0.33) W (sub 0.03) Ti (sub 0.03) Sn (sub 0.02) ) (sub Sigma 0.99) O (sub 4) . The simplified general formula is (Sc,Fe (super 3+) )(Nb,Ta)O (sub 4) . Nioboheftetjernite is monoclinic, P2/c, a=4.7092(3), b=5.6531(4), c=5.0530(4) Aa, beta =90.453(3) degrees , and V=134.515(17) Aa (super 3) . The strongest reflections of the powder X-ray diffraction pattern [d,Aa(I)(hkl)] are: 4.722(22)(100), 3.776(22)(011), 3.628(44)(110), 2:961(100)(111), 2.938(83)(111), 2.472(30)(021), and 1.4497(21)(023,311,132). The crystal structure, refined from single-crystal X-ray diffraction data (R (sub 1) =0.016), is of the "wolframite" type. The mineral is named as the Nb-analogue of heftetjernite, ScTaO (sub 4) .