267 D33. Mineralogy/Crystallography (Posters)

Tuesday, 24 October 2017
9:00 AM - 6:30 PM
Halls 4EF

THE CRYSTAL CHEMISTRY OF BIREFRINGENT UVAROVITE GARNET, IDEALLY CA3CR2SI3O12

Paper number: 267-4
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Extensive research on the anomalous birefringence phenomenon of the garnet-group minerals continues to be the focus and interest of many geoscientists today. Previous studies from over a century of investigations attribute the occurrence of optical anisotropy mostly but not limited to, cation ordering on the dodecahedral {X} and octahedral [Y] sites, lattice mismatch at compositional boundaries caused by strain, and from the presence of hydrous components within the tetrahedral (Z) site. However, the origin remains debatable and is still unclear. Uvarovite, an elusive mantle-derived garnet, ideally, Ca3Cr2Si3O12, is the least studied silicate end-member species. Under crossed polarized light, this beautiful emerald-green mineral displays distinct birefringence of 0.001-0.006 and some crystals exhibit additional anisotropic features such as ‘bowtie’ structure with well defined extinction positions. Birefringent uvarovite from Finland, California, Russia, and Switzerland are investigated using electron-probe micro-analysis (EPMA) and synchrotron high-resolution powder X-ray diffraction (HRPXRD). Our results are consistent with other anisotropic garnets that support the cause of anomalous birefringence in uvarovite garnets, as derived from strain that arise from cubic uvarovite phases consisting of slight variations in chemical compositions.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-301374

© Copyright 2017 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.