Abstract
Synchrotron high-resolution powder X-ray diffraction (HRPXRD), and electron probe microanalysis (EPMA), have been applied in order to study the crystal chemistry and structure of a birefringent almandine (Alm) sample from the Solitude Range, British Columbia. An intergrowth of three and four cubic Alm phases were found for Alm-1 and Alm-2 respectively, along with a minor phase of quartz for both fragments. The a cell parameters in Alm-1 vary between Alm-1a: 11.56615(4) Å and Alm-1c: 11.54858(7) Å. For Alm-2 fragment, the a cell parameters vary between Alm-2a: 11.58726(3) Å and Alm-2d: 11.54978(4) Å. Based on Alm content, compositions range from Alm69.35Grs17.67 Sp7.37Py4.07 to Alm79.98Grs8.12 Py10.52Sp0.08Uv0.04. Based on the cubic symmetry, the peak splitting of the traces observed in the HRPXRD and the heterogeneous Alm composition determined with EPMA, different cubic phases intergrown together is the answer to birefringence in Alm, and could also be in other type of garnets.
