Kangite, (Sc,Ti,Al,Zr,Mg,Ca, )2O3, a new ultra-refractory scandia mineral from the Allende meteorite: Synchrotron micro-Laue diffraction and electron backscatter diffraction

Abstract

Kangite (IMA 2011-092), (Sc,Ti,Al,Zr,Mg,Ca,□)_2O_3, is a new scandia mineral, occurring as micrometer-sized crystals with REE-rich perovskite and spinel in a davisite-dominant ultra-refractory inclusion from the Allende CV3 carbonaceous chondrite. The phase was characterized by SEM, EBSD, synchrotron micro-Laue diffraction, micro-Raman, and EPMA. The mean chemical composition of the type kangite is (wt%) TiO_2 36.6, Sc_2O_3 26.4, ZrO_2 11.3, Al_2O_3 7.0, Y_2O_3 5.4, CaO 3.9, MgO 3.14, Dy_2O_3 1.8, SiO_2 1.7, V_2O_3 1.31, Er_2O_3 0.92, FeO 0.8, Gd_2O_3 0.60, Ho_2O_3 0.40, Tb_2O_3 0.18, Cr_2O_3 0.09, ThO_2 0.04, O −0.3, sum 101.28, which leads to an empirical formula calculated on the basis of 3 O atoms of [(Sc_(0.54)Al_(0.16)Y_(0.07)V_(0.03)Gd_(0.01)Dy_(0.01)Er_(0.01))^(3+)_(∑0.83)(Ti_(0.66)Zr_(0.13))^(4+)_(∑0.79)(Mg_(0.11)Ca_(0.06) Fe_(0.02))^(2+)_(∑0.19) □_(0.19)] _(∑2.00)O_3. Synchrotron micro-Laue diffraction (i.e., an energy scan by a high-flux X-ray monochromatic beam) on one type domain at submicrometer resolution revealed that kangite has a cation-deficient Ia3 bixbyite-type cubic structure. The cell parameters are a = 9.842(1) A, V = 953.3(1) A^3, Z = 16, which leads to a calculated density of 3.879 g/cm^3. Kangite is a new ultra-refractory mineral, likely originating through low-temperature oxidation of a Sc-,Ti^(3+)-enriched high-temperature condensate oxide dating to the birth of the Solar System.