Crystal structure of a birefringent andradite–grossular from Crowsnest Pass, Alberta, Canada. Issue 1 (28th October 2013)

• Record Type: Journal Article
• Authors: Antao, Sytle M.; Klincker, Allison M.
• Is Part Of: Powder diffraction. Volume 29:Issue 1(2014)
• Page Start: 20
• Page End: 27
• Publication Date: 2013-10-28
• Subjects: Powder metallurgy -- Periodicals; Materials -- Analysis -- Periodicals; 620.1127
• DOI: 10.1017/S0885715613001255
• Languages: English
• ISSNs: 0885-7156

Abstract

<abstract abstract-type="normal"> <title> <x content-type="archive" xml:space="preserve">Abstract</x> </title> <p>The structure of a birefringent andradite–grossular sample was refined using single-crystal X-ray diffraction (SCD) and synchrotron high-resolution powder X-ray diffraction (HRPXRD) data. Electron-microprobe results indicate a homogeneous composition of {Ca<sub>2.88</sub>Mn<sup>2+</sup><sub>0.06</sub>Mg<sub>0.04</sub>Fe<sup>2+</sup><sub>0.03</sub>}<sub>Σ3</sub>[Fe<sup>3+</sup><sub>1.29</sub>Al<sub>0.49</sub>Ti<sup>4+</sup><sub>0.17</sub>Fe<sup>2+</sup><sub>0.06</sub>] <sub>Σ2</sub>(Si<sub>2.89</sub>Al<sub>0.11</sub>) <sub>Σ3</sub>O<sub>12</sub>. The Rietveld refinement reduced <italic>χ</italic><sup>2</sup> = 1.384 and overall <italic>R</italic> (<italic>F</italic><sup>2</sup>) = 0.0315. The HRPXRD data show that the sample contains three phases. For phase-1, the weight %, unit-cell parameter (Å), distances (Å), and site occupancy factor (<italic>sof</italic>) are 62.85(7)%, <italic>a</italic> = 12.000 06(2), average <Ca–O> = 2.4196, Fe–O = 1.9882(5), Si–O = 1.6542(6) Å, Ca(<italic>sof</italic>) = 0.970(2), Fe(<italic>sof</italic>) = 0.763(1), and Si(<italic>sof</italic>) = 0.954(2). The corresponding data for phase-2 are 19.14(9)%, <italic>a</italic> = 12.049 51(2), average <Ca–O> = 2.427, Fe–O = 1.999(1), Si–O = 1.665(1) Å, Ca(<italic>sof</italic>) = 0.928(4), Fe(<italic>sof</italic>) = 0.825(3), and Si(<italic>sof</italic>) = 0.964(4). The corresponding data for phase-3 are 18.01(9)%, <italic>a</italic> = 12.019 68(3), average <Ca–O> = 2.424, Fe–O = 1.992(2), Si–O = 1.658(2) Å, Ca(<italic>sof</italic>) = 0.896(5), Fe(<italic>sof</italic>) = 0.754(4), and Si(<italic>sof</italic>) = 0.936(5). The fine-scale coexistence of the three phases causes strain that arises from the unit-cell and bond distances differences, and gives rise to strain-induced birefringence. The results from the SCD are similar to the dominant phase-1 obtained by the HRPXRD, but the SCD misses the minor phases.</p> </abstract>