Crocobelonite, CaFe23+(PO4)2O, a new oxyphosphate mineral, the product of pyrolytic oxidation of natural phosphides

Sergey N. Britvin, Mikhail N. Murashko, Maria G. Krzhizhanovskaya, Natalia S. Vlasenko, Oleg S. Vereshchagin, Yevgeny Vapnik, Vladimir N. Bocharov

Research output: Contribution to journalArticlepeer-review

Abstract

Crocobelonite, CaFe23+(PO4)2O, is a new natural oxyphosphate discovered in the pyrometamorphic complexes of the Hatrurim Formation in Israel and Jordan. Crocobelonite-bearing assemblages contain a series of anhydrous Fe-Ni phosphates, hematite, diopside, anorthite, and phosphides - barringerite Fe2P, transjordanite Ni2P, murashkoite FeP, halamishite Ni5P4, and negevite NiP2. Crocobelonite forms submillimeter-sized aggregates of prismatic to acicular crystals of saffron-red to pinkish-red color. There are two polymorphic modifications of the mineral whose structures are interrelated by the unit-cell twinning. Crocobelonite-2O is orthorhombic, Pnma, a = 14.2757(1), b = 6.3832(1), c = 7.3169(1) Å, V 666.76(1) Å3, Z = 4. This polymorphic modification is isotypic with synthetic oxy-phosphates AV23+ PO42O A where A = Ca, Sr, Cd. The crystal structure has been refined to RB = 0.71% based on powder XRD data, using the Rietveld method and the input structural model obtained from the single-crystal study. Chemical composition (electron microprobe, wt%) is: CaO 16.03, MgO 0.56, Fe2O3 43.37, Al2O3 0.33, SiO2 0.32, P2O5 39.45, Total 100.06. The empirical formula based on O = 9 apfu is Ca 1.02 Fe 1.943+ Mg 0.05 Al 0.022.01 P1.98 Si 0.022.00 O 9.00 with Dcalc = 3.555 cm3. The strongest lines of powder XRD pattern [d(Å)(I)(hkl)] are: 6.54(16)(200), 5.12(26)(201), 3.549(100)(102), 3.200(50) (401), 2.912(19)(220), 2.869(40)(411), 2.662(21)(501). Crocobelonite- 1M is monoclinic, P21/m, a = 7.2447(2), b = 6.3832(1), c = 7.3993(2) Å, β = 106.401(2)°, V = 328.252(14) Å3, Z = 2. This polymorphic modification does not have direct structural analogs. Its crystal structure has been solved and refined based on the single-crystal data to R1 = 1.81%. Chemical composition is: CaO 15.56, MgO 0.16, NiO 0.78, Fe2O3 41.28, Al2O3 0.45, V2O3 0.42, Cr2O3 0.23, TiO2 0.79, P2O5 39.94, Total 99.61, corresponding to the empirical formula (O = 9 a p f u) Ca 0.99 Fe 1.853+ Ni 0.04 Ti 0.04 Al 0.03 V 0.023 + Cr 0.01 Mg 0.012.00 P 2.01 O 9.00 with Dcalc = 3.604 g/cm3. The strongest lines of powder XRD pattern [d(Å)(I)(hkl)] are 6.98(17)(100), 4.40(22)(101), 3.547(100)(201), 3.485(21)(200), 3.195(50)(020), 2.855(38)(102), 2.389(33)(122). Crocobelonite represents a novel type of phosphate mineral formed by oxidation of phosphide minerals at temperatures higher than 1000 °C and near-atmospheric pressure (pyrolytic oxidation).

Original languageAmerican English
Pages (from-to)1973-1983
Number of pages11
JournalAmerican Mineralogist
Volume108
Issue number10
DOIs
StatePublished - 1 Oct 2023

Keywords

  • crystal structure
  • Dead Sea
  • Hatrurim Formation
  • Middle East
  • new mineral
  • oxophosphate
  • oxyphosphate
  • Phosphate
  • phosphide
  • pyrolytic oxidation
  • pyrometamorphism

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

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