Nelson, Stephen A. (Fall 2008). "Weathering & Clay Minerals". Professor's lecture notes (EENS 211, Mineralogy). Tulane University. Archived from the original on 1 August 2017. Retrieved 13 November 2008.
"spar". Oxford English Dictionary. Oxford Dictionaries. Archived from the original on 26 September 2016. Retrieved 13 January 2018.
Nelson, Stephen A. (Fall 2008). "Weathering & Clay Minerals". Professor's lecture notes (EENS 211, Mineralogy). Tulane University. Archived from the original on 1 August 2017. Retrieved 13 November 2008.