Citation: Fregola, R. A.; Skogby, H.; Bosi, F.; D'Ippolito V; Andreozzi, G. B.; Halenius, U. (2014). Optical absorption spectroscopy study of the causes for color variations in natural Fe-bearing gahnite: Insights from iron valency and site distribution data Note: Sample Sp2781_6c. American Mineralogist, 99, pp. 2187-2195.