Effect of Thermal Treatment on the Cation Exchange and Disordering in Tourmaline

University of Vermont ScholarWorks @ UVM Graduate College Dissertations and Theses Dissertations and Theses 2014 Effect Of Thermal Treatment On The aC tion Exchange And Disordering In Tourmaline Jacob Stern Menken University of Vermont Follow this and additional works at: https://scholarworks.uvm.edu/graddis Part of the Geology Commons Recommended Citation Menken, Jacob Stern, "Effect Of Thermal Treatment On The aC tion Exchange And Disordering In Tourmaline" (2014). Graduate College Dissertations and Theses. 254. https://scholarworks.uvm.edu/graddis/254 This Thesis is brought to you for free and open access by the Dissertations and Theses at ScholarWorks @ UVM. It has been accepted for inclusion in Graduate College Dissertations and Theses by an authorized administrator of ScholarWorks @ UVM. For more information, please contact [email protected]. EFFECT OF THERMAL TREATMENT ON THE CATION EXCHANGE AND DISORDERING IN TOURMALINE A Thesis Presented by Jacob S. Menken To The Faculty of the Graduate College Of The University of Vermont In Partial Fulfillment of the Requirements For the Degree of Master of Sciences Specializing in Geology October, 2014 Accepted by the Faculty of the Graduate College, The University of Vermont, in partial fulfillment of the requirements for the degree of Master of Science, specializing in Geology. Thesis Examination Committee: _____________________________ Advisor John M. Hughes, PhD. _____________________________ Laura E. Webb, PhD. _____________________________ Chairperson Donald S. Ross, PhD. _____________________________ Dean, Graduate College Cynthia J. Forehand, PhD. May 13, 2014 Abstract Tourmaline is an aluminoborocyclosilicate mineral with a complex arrangement of atoms. With highly variable chemistry and multiple cation sites, tourmaline is one of the last complex minerals whose structure was unraveled, and its response to changes in Pressure-Temperature-Time (P-T-X) are not well understood. Due to its stability at high temperature and pressure, tourmaline has the potential to be an informative mineral in terms of petrogenetic indicators and could be used in assessing provenance, thermobarometry and geochronology. Three reactions were proposed to understand the cation exchange and disordering between the Y- and Z-sites in the tourmaline structure. These reactions include: 1. YFe2+ + ZAl + OH ↔ ZFe3+ + YAl + O + H↑ in two samples with varying Fe2+ content. 2. YMg + ZAl ↔ ZMg + YAl. 3. YFe3+ + ZAl ↔ ZFe3+ + YAl. Using single crystal X-ray diffraction and stepwise heating, the extent and effect of the exchange between the Y- and Z-sites in response to changes in temperature was described. In response to increased temperature, equivalent amounts of Fe2+, Fe3+, Mg2+ of the Y-sites exchange with Al of the Z-sites. This leads to decreases in Y-site average bond length, increases in Z-site average bond length, shortening of a lattice parameters, lengthening of c lattice parameters and decreases in quadratic elongation. Additionally, the T-site experienced an increased in tetrahedral rotation and ditrigonality and changes to the crimping of the tetrahedral ring upon heating. The cation exchange and disordering in these samples relates to the stability of tourmaline at elevated temperatures in that tourmaline will undergo cation exchange and disordering to maintain the stability of the mineral. This has implications on the conditions in which tourmaline is formed as well as stability of tourmaline and other minerals and materials in different P-T-X conditions. ACKNOWLEDGEMENTS I would like to thank my advisor and mentor, Dr. John M. Hughes, for his patience, guidance and mentorship through my undergraduate and graduate education. His belief in my abilities has allowed me to achieve everything I have today. I owe my passion for minerals and my career in the geosciences to him. I would also like to thank the rest of my committee, Dr. Laura E. Webb and Chairman Dr. Donald S. Ross for the education they have provided me in years I have been their student and their time and effort throughout the thesis process. I would also like to thank the rest of University of Vermont Department of Geology faculty for the lessons both in and out of the classroom that they have imparted on me over the years. Special acknowledgement to Dr. Andreas Ertl for providing three of the samples used in experimentation as well as numerous thoughts and comments on the thesis. A thank you goes out to Alan Howard, Lane Manning, Erin Wood and Todd Cramer for advisement and assistance at various times throughout this process. This research is funded by the National Science Foundation (NSF-MRI 1039436 awarded to JMH). The graduate students of the geology department deserve an acknowledgement for their support and friendship throughout the stress and difficulty the last two years has provided us all. Gina and the rest of the research group deserve the highest praise and thanks for their assistance and support. Finally, I would like to acknowledge the friends I have had at UVM, as well as my family and my one in a million girlfriend, S.J.H., for their support, understanding and belief in me. I could not have done this without you. Thank you everyone for the incredible experience. ii TABLE OF CONTENTS ACKNOWLEDGEMENTS……………………………………………………………….ii LIST OF TABLES………………………………………………………………………...v LIST OF FIGURES……………………………………………………………………...vii CHAPTER 1: INTRODUCTION…………………………………………………………1 CHAPTER 2: BACKGROUND…………………………………………………………..3 2.1. Tourmaline……………………………………………………………………………3 2.2. Previous Work………………………………………………………………………10 CHAPTER 3: METHODS……………………………………………………………….12 3.1. Sample Selection…………………………………………………………………….12 3.2. Heating………………………………………………………………………………15 3.3. Crystal Structure…………………………………………………………………….15 CHAPTER 4: RESULTS...................................................................................................19 4.1. TK1C10 (Fe2+-rich)…………………………………………………………………19 4.2. TK1R1 (Fe2+-rich)…………………………………………………………………..29 4.3. DRFR (Mg2+-rich)…………………………………………………………………..39 4.4. 10689 (Fe3+-rich)……………………………………………………………………47 CHAPTER 5: DISCUSSION…………………………………………………………….57 5.1. Effect of Heating on Polyhedral Bond Lengths...…………………………………...57 5.2. Effect of Heating on Y- and Z-Site Occupancy and Disordering……………………60 iii 5.3. Effect of Heating on Lattice Parameters…………………………………………….67 5.4. Effect of Heating on T-Site Tetrahedra ……………………………………………..71 5.5. Effect of Heating on Distortions…………………………………………………….78 5.6. Effect of Heating on Stability……………………………………………………….83 CHAPTER 6: CONCLUSION…………………………………………………………..89 REFERENCES…………………………………………………………………………..94 iv LIST OF TABLES Table 1: Tourmaline constituents and bonding site nomenclature following Hawthorne & Henry (1999)………………………………………………………………………………7 Table 2: Tourmaline species chemistries and cation distribution…………………………8 Table 3: Chemistries and cation distribution of samples used in this study prior to heating……………………………………………………………………..……………..14 Table 4: Crystallographic data for all analyzed samples………………………………...16 Table 5: Atomic coordinates and equivalent isotropic atomic displacement for sample TK1C10…………………………………………………………………………………..21 Table 6: Selected bond lengths (Å) for sample TK1C10………………………………...24 Table 7: Occupancy of the Y- and Z-sites for sample TK1C10……………………….…25 Table 8: Atomic coordinates and equivalent isotropic atomic displacement for sample TK1R1……………………………………………………………………………………31 Table 9: Selected bond lengths (Å) for sample TK1R1………………………………….34 Table 10: Occupancy of the Y- and Z-sites for sample TK1R1………..………………...35 Table 11: Atomic coordinates and equivalent isotropic atomic displacement for sample DRFR…………………………………………………………………………………….41 Table 12: Selected bond lengths (Å) for sample DRFR…………………………………43 Table 13: Atomic coordinates and equivalent isotropic atomic displacement for sample 10689…………………………………………………………………………………......49 Table 14: Selected bond lengths (Å) for sample 10689….………………………………52 Table 15: Occupancy of the Y- and Z-sites for sample 10689…………………………...53 Table 16: Site occupancy of the Y- and Z-sites at initial and final conditions for all samples…………………………………………………………………………………...66 Table 17: Lattice parameters a and c (Å) for all samples at each temperature (°C)…......67 Table 18: Tetrahedral rotation (°) of all samples at each temperature (°C)……………...72 v Table 19: Crimping (Δz) of the T-site tetrahedra for of all samples at each temperature step (°C)………………………………………………………………………………….74 Table 20: Ditrigonality (δ) of the T-site tetrahedra for of all samples at each temperature step (°C)………………………………………………………………………………….75 Table 21: Polyhedron distortion of all samples at each temperature (°C)……………….79 Table 22: Bond valence sums for the Y- and Z-sites……………………………………..86 vi LIST OF FIGURES Figure 1a: Tourmaline structural components projected down the c axis with the a axis horizontal………………………………………………………………………………….4 Figure 1b: Tourmaline structural components projected with the a axis horizontal and the c axis vertical……………………………………………………………………………...4 Figure 2a: Ball-and-stick model of shared edges between the Y-site and Z-site O3 and O6 oxygen atoms……………………………………………………………………………...5 Figure 2b: Polyhedral model of shared edges between the Y-site and Z-site O3 and O6 oxygen atoms……………………………………………………………………………...5 Figure 3: Pressure-temperature plot of tourmaline stability………………………………9 Figure 4a: Average Y-O bond length (Å) for each temperature step (°C) for sample TK1C10…………………………………………………………………………………..25 Figure 4b: Average Z-O

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