Heamanite-(Ce), (K0.5Ce0.5)TiO3, a new perovskite supergroup mineral found in diamond from Gahcho Kué, Canada
-
Chiara Anzolini
, William K. Siva-Jothy
, Tonči Balić-Žunić
, Ingrid L. Chinn
Abstract
Heamanite-(Ce) (IMA 2020-001), ideally (K0.5Ce0.5)TiO3, is a new perovskite-group mineral found as an inclusion in a diamond from the Gahcho Kué mine in the Northwest Territories, Canada. It occurs as brown, translucent single crystals with an average maximum dimension of ~80 μm, associated with rutile and calcite. The luster is adamantine, and the fracture conchoidal. Heamanite-(Ce) is the K-analog of loparite-(Ce), ideally (NaCe)Ti2O6. The Mohs hardness is estimated to be 5½ by comparison to loparite-(Ce), and the calculated density is 4.73(1) g/cm3. Electron microprobe wavelength-dispersive spectrometric analysis (average of 34 points) yielded: CaO 10.70, K2O 7.38, Na2O 0.16, Ce2O3 13.77, La2O3 8.22, Pr2O3 0.84, Nd2O3 1.59, SrO 6.69, BaO 2.96, ThO2 0.36, PbO 0.15, TiO2 45.77, Cr2O3 0.32, Al2O3 0.10, Fe2O3 0.09, Nb2O5 0.87, UO3 0.01, total 99.98 wt%. The empirical formula, based on 3 O atoms, is: [(K0.268Na0.009)Σ0.277(Ce0.143La0.086Pr0.009Nd0.016)Σ0.254(Ca0.326Sr0.110Ba0.033Pb0.001)Σ0.470Th0.002]Σ1.003 (Ti0.979Nb0.011Cr0.007Al0.003Fe0.002)Σ1.002O3. The Goldschmidt tolerance factor for this formula is 1.003. Heamanite-(Ce) is cubic, space group Pm3m, with unit-cell parameter a = 3.9129(9) Å, and volume V = 59.91(4) Å3 (Z = 1). The crystal structure was solved using single-crystal X‑ray diffraction data and refined to R1(F) = 2.61%. Heamanite-(Ce) has the aristotypic perovskite structure and adopts the same structure as isolueshite and tausonite. The six strongest diffraction lines are [dobs in angstroms (I in percentages) (hkl)]: 2.764 (100) (110), 1.954 (41) (200), 1.596 (36) (211), 1.045 (16) (321), 1.236 (13) (310), and 1.382 (10) (220). The Raman spectrum of heamanite-(Ce) shows two broad bands at 560 and 787 cm−1, with no bands observed above 1000 cm−1. Heamanite-(Ce) is named after Larry Heaman, a renowned scientist in the field of radiometric dating applied to diamond-bearing kimberlites, mantle-derived eclogites, and lamprophyre dikes. The dominant REE should appear as a Levinson suffix, hence heamanite-(Ce).
Funding statement: This research was financially supported by a Canada Excellence Research Chair (CERC) grant to D.G.P., a Natural Sciences and Engineering Research Council Discovery Grant to T. S., and by the Diamond Exploration and Research Training School (DERTS), all funded by NSERC. M.A. acknowledges support from the Italian Ministry for Research and University–Scientific Independence of Young Researchers (MIUR-SIR) MILE DEEp project (grant no. RBSI140351) and the ERC-StG 2016 TRUE DEPTHS (grant no. 714936).
Acknowledgments
C.A. thanks Marta Morana for assistance during the X‑ray data collection and Luca Peruzzo for help with the Vickers microhardness test. De Beers Group is thanked for donating the diamond specimen from its Gahcho Kué mine. We thank three anonymous reviewers for suggestions that led to the improvement of the manuscript, and Jennifer Kung for careful editorial handling.
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Articles in the same Issue
- Estimating kaolinite crystallinity using near-infrared spectroscopy: Implications for its geology on Earth and Mars
- The interplay between twinning and cation inversion in MgAl2O4-spinel: Implications for a nebular thermochronometer
- The effect of fluorine on reaction-rim growth dynamics in the ternary CaO-MgO-SiO2 system
- Seeing through metamorphic overprints in Archean granulites: Combined high-resolution thermometry and phase equilibrium modeling of the Lewisian Complex, Scotland
- Interphase misorientation as a tool to study metamorphic reactions and crystallization in geological materials
- Trace element partitioning between olivine and melt in lunar basalts
- Solving the iron quantification problem in low-kV EPMA: An essential step toward improved analytical spatial resolution in electron probe microanalysis—Fe-sulfides
- Zircon geochronological and geochemical insights into pluton building and volcanic-hypabyssal-plutonic connections: Oki-Dōzen, Sea of Japan—A complex intraplate alkaline volcano
- Using cathodoluminescence to identify oscillatory zoning of perthitic K‑feldspar from the equigranular Toki granite
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- A revised analysis of ferrihydrite at liquid helium temperature using Mössbauer spectroscopy
- First find of merrillite, Ca3(PO4)2, in a terrestrial environment as an inclusion in lower-mantle diamond
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