Haggertyite, a new magnetoplumbite-type titanate mineral from the Prairie Creek (Arkansas) lamproite

We describe a new titanate mineral, haggertyite, from the Prairie Creek lam proite, Arkansas, U.S.A. The mineral was found exclusively within the react ion zones surrounding small mafic xenoliths in the lamproite. Haggertyite o ccurs as isolated platelets, typically 30-70 mu m maximum dimension, which often show hexagonal morphology. Associated minerals are diopside, olivine, phlogopite, Ti-K-richterite, chrome spinel, ilmenite, priderite, and jeppe ite. Haggertyite has a magnetoplumbite-type structure. Typical microprobe a nalyses give (as wt% oxides) TiO2 = 36.5-41.6, FeO = 39.4-42.9, MgO = 0.7-3 .6, BaO = 9.5-10.5, K2O = 1.3-1.5, Cr2O3 = 0.0-5.6, MnO = 0.6-1.1, and NiO = 0.1-0.4. The average composition (based on 19 O atoms and an Fe2+/Fe3+ ra tio to give 12 small cations) is Ba0.68K0.31Ti5.05Fe3.912+Fe2.013+Mg0.69(Cr ,Mn,N)(0.34)O-19. Haggertyite is hexagonal, space group P6(3)/mmc, Z = 2, a = 5.9369(1), c = 23.3445(6) Angstrom, calculated density of 4.74 g/ cm). T he structure was refined to R-1 = 0.034 for 339 unique reflections with F-o > 4 sigma(Fo) using single-crystal data. Strongest reflections are [d(calc ) (Angstrom), I-calc, hkl] 2.641 100% (114), 2.795 90% (017), 1.634 47% (02 ,11), 2.437 46% (023), and 2.963 44% (110). In reflected light, haggertyite is pale gray, opaque, and without internal reflections. It is not discerna bly pleochroic or bireflectant, but it is weakly anisotropic in shades of d ark brown. Quantitative specular reflectance measurements for Ro and Re' in air and in oil immersion, respectively, are: 470 nm, 17.3, 16.9, and 5.37, 5.13%; for 546 nm 16.8, 16.35, and 5.19, 4.90%; for 589 nm 16.9, 16.3, and 5.29, 4.92%; and for 650 nm 17.1, 16.4, and 5.42, 5.00%. VHN50 = 500, with a range of five indentations = 460-540. The mineral is named for Stephen E . Haggerty in honor of his contributions to the mineralogy and crystal chem istry of upper-mantle titanate minerals.