Master of Science
Dr. Roberta Flemming
Al-,Ti-rich diopside, referred to herein as fassaite, occurs in both terrestrial and extraterrestrial environments. The composition of fassaite, Ca(Mg,Al)(Si,Al)2O6, makes it ideal for Al/Si cation ordering studies. In this study, crystal XRD, 27Al and 29Si MAS NMR as well as 27Al 3QMAS NMR is used to study cation ordering in extraterrestrial fassaite from Allende CAIs and a terrestrial analogue from Fassa Valley Italy. From 27Al and 29Si spectroscopy, fassaite from Allende CAIs is found to have more local Al/Si cation ordering than terrestrial Fassaite. Both terrestrial and extraterrestrial have C2/c symmetry indicating long range cation disorder. Completely ordered fassaite has never been found in nature. The local ordering in the Allende fassaite likely indicates ordering above the disorder/ order transition temperature. Cation ordering could provide an independent estimate of temperature and cooling rate on the Allende parent body, once the transformation temperature is known.
Haring, Monika M., "Crystal Structure and Al/Si Cation Ordering in "Fassaite": A Combined Single Crystal, 27Al and 29Si NMR Study" (2012). Electronic Thesis and Dissertation Repository. Paper 1058.