Abstract
Nataliakulikite, Ca4Ti2(Fe3+,Fe2+)(Si,Fe3+,Al)O11, is a mineral intermediate between perovskite CaTiO3 and brownmillerite Ca2(Fe,Al)2O5. It was discovered as a minor mineral in a high-temperature pyrometamorphic larnite-gehlenite rock at the Nahal Morag Canyon of the Hatrurim Basin, Israel. Nataliakulikite is associated with larnite, flamite, gehlenite, magnesioferrite, Fe3+-rich perovskite, fluorapatite, barite, Hashemite, and retrograde phases (afwillite, hillebrandite, portlandite, calcite, ettringite, hydrogarnet, and other hydrated Ca-silicates). The mineral forms brown subhedral or prismatic grains (up to 20 µm) and their intergrowths (up to 50 μm). Its empirical formula (n = 47) is (Ca3.992Sr0.014U0.004)(Ti1.933Zr0.030Nb0.002) (Fe3+0.610Fe2+0.405Cr0.005Mn0.005)(Si0.447Fe3+0.337Al0.216)O11 and shows Si predominance in tetrahedral site. The unit-cell parameters (HRTEM data) and space group are: a = 5.254, b = 30.302, c = 5.488 Å, V = 873.7 Å3, Pnma, Z = 4. These dimensions and Electron backscatter diffraction (EBSD) data strongly support the structural identity between nataliakulikite and synthetic Ca4Ti2Fe3+2O11 (2CaTiO3∙Ca2Fe3+2O5), an intermediate compound in the system CaTiO3-Ca2Fe3+2O5. In general, this mineral is a Si-Fe2+-rich natural analog of synthetic Ca4Ti2Fe3+2O11. The X-ray powder diffraction data (CuKα -radiation), calculated from unit-cell dimensions, show the strongest lines {d [Å], (Icalc)} at: 2.681(100), 1.898(30), 2.627(26), 2.744(23), 1.894(22), 15.151(19), 1.572(14), 3.795(8). The calculated density is 4.006 g/cm3. The crystal structure of nataliakulikite has not been refined because of small sizes of grains. The Raman spectrum shows strong bands at 128, 223, 274, 562, and 790 cm−1. Nataliakulikite from the Hatrurim Basin crystallized under the conditions of combustion metamorphism at high temperatures (1160–1200 °C) and low pressures (HT-region of the spurrite-merwinite facies).
Highlights
The natural Si-Fe2+ -rich analog of the orthorhombic synthetic phase Ca4 Ti2 Fe3+ 2 O11, an intermediate member between perovskite CaTiO3 and brownmillerite Ca2 FeAlO5, named nataliakulikite, was discovered in a larnite-gehlenite rock at the Hatrurim Basin, the largest combustion metamorphism complex of the Hatrurim Formation on the territory of Israel [1,2,3,4,5].Synthetic Fe2 O3 (Fe)-rich compounds based on the perovskite and brownmillerite structures (“layered perovskites”) have been intensively studied in material sciences due to their superconductivity and ion-conductivity properties [6,7]
Nataliakulikite Ca4 Ti2 (Fe3+,Fe2+ )(Si,Fe3+,Al2 O3 (Al))O11 was approved by the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA) as a new mineral species in September 2018 (IMA 2018-061)
We provide a detailed description of nataliakulikite
Summary
The natural Si-Fe2+ -rich analog of the orthorhombic synthetic phase Ca4 Ti2 Fe3+ 2 O11 , an intermediate member between perovskite CaTiO3 and brownmillerite Ca2 FeAlO5 , named nataliakulikite, was discovered in a larnite-gehlenite rock at the Hatrurim Basin, the largest combustion metamorphism complex of the Hatrurim Formation on the territory of Israel [1,2,3,4,5].Synthetic Fe-rich compounds based on the perovskite and brownmillerite structures (“layered perovskites”) have been intensively studied in material sciences due to their superconductivity and ion-conductivity properties [6,7]. The natural Si-Fe2+ -rich analog of the orthorhombic synthetic phase Ca4 Ti2 Fe3+ 2 O11 , an intermediate member between perovskite CaTiO3 and brownmillerite Ca2 FeAlO5 , named nataliakulikite, was discovered in a larnite-gehlenite rock at the Hatrurim Basin, the largest combustion metamorphism complex of the Hatrurim Formation on the territory of Israel [1,2,3,4,5]. Three synthetic ordered phases, intermediate between brownmillerite Ca2 FeAlO5 and perovskite CaTiO3 , are known: Ca4 Ti2 Fe3+ 2 O11 [8,9], Ca3 TiFe3+ 2 O8 [10,11,12], and Ca5 TiFe3+ 2 Al2 O13 [13].
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