Two cubic phases in kimzeyite garnet from the type locality Magnet Cove, Arkansas

Journal Article · Tue Nov 08 00:00:00 EST 2016 · Acta Crystallographica. Section B, Structural Science, Crystal Engineering and Materials (Online)

DOI:https://doi.org/10.1107/S2052520616014700· OSTI ID:1340709

Antao, Sytle M.; Cruickshank, Laura A.

The crystal structure of an optically anisotropic kimzeyite garnet from Magnet Cove, Arkansas, USA, where it was first discovered, was refined with the Rietveld method, cubic space group, Ia\overline 3 d, and monochromatic [λ = 0.41422 (2) Å] synchrotron high-resolution powder X-ray diffraction (HRPXRD) data. The Rietveld refinement reduced χ²and overallR(F²) values are 1.840 and 0.0647, respectively. The sample, with the general garnet formula^[8]X₃^[6]Y₂^[4]Z₃^[4]O₁₂, contains an intergrowth of two cubic phases that occur initially as oscillatory growth zoning, and patchy intergrowths arise later from fluid-enhanced dissolution and re-precipitation. The two compositions obtained with electron-probe microanalyses (EPMA) are Ca_3.00(Zr_1.31Ti⁴⁺_0.46Fe³⁺_0.22Mn³⁺_0.01)_Σ2[Al_0.76Fe³⁺_1.01Si_1.23]_Σ3O₁₂for phase 1aand Ca_2.99(Zr_1.48Ti⁴⁺_0.37Fe³⁺_0.15)_Σ2[Al_0.87Fe³⁺_0.98Si_1.15]_Σ3O₁₂for phase 1b. The weight percentage, unit-cell parameter (Å), distances (Å), and site occupancy factors (s.o.f.s) for phase 1aare as follows: 42.6 (2)%,a= 12.46553 (3) Å, average <X—O> = 2.482,Y—O = 2.059 (2),Z—O = 1.761 (2) Å, Ca (Xs.o.f.) = 0.960 (4), Zr (Ys.o.f.) = 0.809 (3), and Fe (Zs.o.f.) = 0.623 (2). The corresponding values for phase 1bare 57.4 (2)%,a= 12.47691 (2) Å, average <X—O> = 2.482,Y—O = 2.062 (1),Z—O = 1.762 (1) Å, Ca (Xs.o.f.) = 0.957 (3), Zr (Ys.o.f.) = 0.828 (2) and Fe (Zs.o.f.) = 0.617 (2). The main structural differences between the two phases are in the unit-cell parameter, Δa= 0.01138 Å,Y(s.o.f.), andY—O distance. Structural mismatch between the two cubic phases in a crystal gives rise to strain-induced optical anisotropy.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
• Sponsoring Organization: USDOE
• OSTI ID: 1340709
• Journal Information: Acta Crystallographica. Section B, Structural Science, Crystal Engineering and Materials (Online), Vol. 72, Issue 6; ISSN 2052-5206
• Publisher: International Union of Crystallography
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

36 MATERIALS SCIENCE