@article{gualda_vlach_2005,  title={Stoichiometry-based estimates of ferric iron in calcic, sodic-calcic and sodic amphiboles: a comparison of various methods},  volume={77},  ISSN={0001-3765},  url={https://doi.org/10.1590/S0001-37652005000300012},  DOI={10.1590/S0001-37652005000300012},  number={3},  journal={Anais da Academia Brasileira de Ciências},  publisher={Academia Brasileira de Ciências},  author={Gualda, Guilherme A.R. and Vlach, Silvio R.F.},  year={2005},  month={Sep},  pages={521–534} }