Microstructural Investigation of Evaporitic Silica

点击翻译按钮获取中文摘要

Heaney 9418031 The funds requested in this proposal will support Professor Peter J. Heaney of Princeton University and his research group in their investigations of microcrystalline silica SiO2 . This work will explore the ways in which silica microstructures reflect the chemistry of the environments in which they formed. Although these kinds of investigations have been intensively pursued for biogenic marine silica, the structural characteristics of silica minerals from evaporitic environments remain relatively unknown. Our ignorance of these phases is especially unfortunate, since evaporitic silica is an important paleoclimatic indicator and is commonly associated with economic ores. By using transmission electron microscopy, powder X-ray diffraction, and electron probe microanalysis, Heaney and coworkers will determine the way in which evaporitic silica forms and transforms over time. These studies will involve three interrelated projects: 1) Microstructural analysis of moganite, a newly recognized silica polymorph; 2) Determination of the crystal structure of the hydrous sodium silicate magadiite and the structural pathway between magadiite and moganite; and 3) Examination of replacement mechanisms between evaporitic silica and preexisting carbonate. This work will establish a microstructural understanding of the diagenetic alteration of silica minerals from evaporitic deposits, and it will reveal silicification mechanisms of shell carbonate at the atomic scale and should shed light on fossilization processes.