Barioferrite BaFe12O19: A new mineral species of the magnetoplumbite group from the Haturim Formation in Israel

Abstract

A new mineral barioferrite—a natural analogue of synthetic barium ferrite Ba Fe 12 3+ O19—has been identified in the central part of a metamorphosed barite nodule in the rock of the Haturim Formation (Mottled Zone) on the southern slope of Mount Ye’elim in Israel. The mineral is associated with barite, calcite, magnetite, and maghemite and occurs as tiny platy crystals up to 3 × 15 × 15 μm and their irregular aggregates. Barioferrite is black with streaks of brown, and its luster is submetallic. Its Calculated density is 5.31 g/cm3. The mineral is brittle; cleavage is absent. IR absorption bands (cm−1) are observed at 635 (shoulder), 582, 544, 433, and 405 (shoulder). Barioferrite is characterized by ferrimagnetic behavior. Under a microscope in reflected light, barioferrite is grayish white with brownish red internal reflections, the pleochroism is weak (from gray-white on R o to gray-white with a brown tint on R e), and the bireflectance is weak with distinct anisotropy. The reflectance values of R o/R e, % (λ, nm) are 24.51/22.80 (470), 24.17/22.25 (546), 23.65/21.68 (589), and 22.67/20.85 (650). The chemical composition (electron microprobe, wt %; the ranges are given in parentheses) is BaO 13.13 (12.5–13.8), Fe2O3 86.47 (85.5–87.5), and 99.60 in total. The empirical formula is Ba0.95Fe 12.03 3+ O19. Barioferrite is hexagonal with space group P63/mmc, a = 5.875 (3) A, c = 23.137 (19) A, V = 691.6 (5) A3, and Z = 2. The strongest lines of the X-ray powder diffraction pattern [d, A, (I, 5) (hkl)] are 2.938(46) (110), 2.770(100) (107), 2.624 (84) (114, 200), 2.420(44) (203), 2.225(40) (205), and 1.627(56) (304, 2.0.11). The holotype specimen of barioferrite is deposited at the Mineralogical Museum of St. Petersburg State University; its catalogue number is 1/19436.