GSA Annual Meeting in Seattle, Washington, USA - 2017

Paper No. 267-14
Presentation Time: 9:00 AM-6:30 PM

POVONDRAITE CRYSTAL CHEMISTRY


CLARK, Christine M.1, SCHIFFERT, Matthew P.1 and CYMES, Brittany A.2, (1)Dept. of Geography and Geology, Eastern Michigan University, Ypsilanti, MI 48197, (2)Geology & Environmental Earth Science, Miami University, 500 E. High Street, Oxford, OH 45056, cclark7@emich.edu

The tourmaline super-group has a general chemical formula of XY3Z6 (T6O18) (BO3)3 V3W, and povondraite is a species of tourmaline with a formula of NaFe3+3(Fe3+4Mg2) Si6O18 (BO3)3 (OH)3O. Through standard normalization procedures, multiple researchers have reported quantities of greater than 1 apfu in the X-site in povondraite. Several different explanations for this anomaly have been explored, including incorrect Fe2+/Fe3+ ratios, [4]B, and OH+F sums. These could all change the normalized values, however they fail to explain the variance seen in povondraite, as any normalization scheme which would lower the X-site cation value also lowers all other cations, resulting in apparent vacancies in other cation sites, which has never been reported for tourmaline. We have collected S-XRD and TEM data on samples of povondraite and EMPA data from several different labs in order to try to isolate the cause of the reported anomaly.