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Nixonite (IMA 2018-133), ideally Na 2 Ti 6 O 13 , is a new mineral found within a heavily metasomatized pyroxenite xenolith from the Darby kimberlite field, beneath the west-central Rae Craton, Canada. It occurs as microcrystalline aggregates, 15 to 40 mm in length. Nixonite is isostructural with jeppeite, K 2 Ti 6 O 13 , with a structure consisting of edge- and corner-shared titanium-centered octahedra that enclose alkali-metal ions. The Mohs hardness is estimated to be between 5 and 6 by comparison to jeppeite, and the calculated density is 3.51(1) g/cm 3 . Electron microprobe wavelength-dispersive spectroscopic analysis (average of 6 points) yielded: Na 2 O 6.87, K 2 O 5.67, CaO 0.57, TiO 2  84.99, V 2 O 3  0.31, Cr 2 O 3  0.04, MnO 0.01, Fe 2 O 3  0.26, SrO 0.07, total 98.79 wt%. The empirical formula, based on 13 O atoms, is: (Na 1.24 K 0.67 Ca 0.06 ) S1.97 (Ti 5.96 V 0.023 Fe 0.018 ) S6.00 O 13  with minor amounts of Cr and Mn. Nixonite is monoclinic, space group  C 2/ m , with unit-cell parameters  a  = 15.3632(26) Å,  b  = 3.7782(7) Å,  c  = 9.1266(15) Å, b = 99.35(15)°, and  V  = 522.72(1) Å 3 , Z = 2. Based on the average of seven integrated multi-grain diffraction images, the strongest diffraction lines are [ d  obs  in Å ( I  in %) ( hkl )]: 3.02 (100) (310), 3.66 (75) (110), 7.57 (73) (200), 6.31 (68) (201), 2.96 (63) (311), 2.96 (63) (203), and 2.71 (62) (402). The five main Raman peaks of nixonite, in order of decreasing intensity, are at 863, 280, 664, 135, and 113 cm –1 . Nixonite is named after Peter H. Nixon, a renowned scientist in the field of kimberlites and mantle xenoliths. Nixonite occurs within a pyroxenite xenolith in a kimberlite, in association with rutile, priderite, perovskite, freudenbergite, and ilmenite. This complex Na-K-Ti-rich metasomatic mineral assemblage may have been produced by a fractionated Na-rich kimberlitic melt that infiltrated a mantle-derived garnet pyroxenite and reacted with rutile during kimberlite crystallization.

Nixonite, Na 2 Ti 6 O 13 , a new mineral from a metasomatized mantle garnet pyroxenite from the western Rae Craton, Darby kimberlite field, Canada