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An Investigation Into the UV Fluorescence of Feldspar Group

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An Investigation Into the UV Fluorescence of Feldspar Group An Investigation into UV Fluorescence in Feldspar Group Minerals Natasha Morrison Submitted in Partial Fulfillment of the Requirement for the Degree of Honours Bachelor of Science, Department of Earth Sciences At Dalhousie University Halifax, Nova Scotia March 17th, 2013 Submitted to: Dr. Richard Cox Dr. Martin Gibling 1 Distribution License DalSpace requires agreement to this non-exclusive distribution license before your item can appear on DalSpace. NON-EXCLUSIVE DISTRIBUTION LICENSE You (the author(s) or copyright owner) grant to Dalhousie University the non-exclusive right to reproduce and distribute your submission worldwide in any medium. You agree that Dalhousie University may, without changing the content, reformat the submission for the purpose of preservation. You also agree that Dalhousie University may keep more than one copy of this submission for purposes of security, back-up and preservation. You agree that the submission is your original work, and that you have the right to grant the rights contained in this license. You also agree that your submission does not, to the best of your knowledge, infringe upon anyone's copyright. If the submission contains material for which you do not hold copyright, you agree that you have obtained the unrestricted permission of the copyright owner to grant Dalhousie University the rights required by this license, and that such third-party owned material is clearly identified and acknowledged within the text or content of the submission. If the submission is based upon work that has been sponsored or supported by an agency or organization other than Dalhousie University, you assert that you have fulfilled any right of review or other obligations required by such contract or agreement. Dalhousie University will clearly identify your name(s) as the author(s) or owner(s) of the submission, and will not make any alteration to the content of the files that you have submitted. If you have questions regarding this license please contact the repository manager at [email protected]. Grant the distribution license by signing and dating below. Name of signatory Date lmJ DALHOUSIE Department of Earth Sciences \!I UNIVERSITY Halifax, Nova Scotia Inspiring Minds Canada B3H 4R2 (902) 494-2358 FAX (902) 494-6889 DATE: Mr' I 2Z !Z01LJ AUTHOR: TITLE: Degree: Convocation: --'i--'-\'-"0:_:_\/1--- Year: Z01y Pennission is herewith granted to Dalhousie University to circulate and to have copied for non-commercial purposes, at its discretion, the above title upon the request of individuals or institutions. THE AUTHOR RESERVES OTHER PUBLICATION RIGHTS, AND NEITHER THE THESIS NOR EXTENSIVE EXTRACTS FROM IT MAY BE PRINTED OR OTHERWISE REPRODUCED WITHOUT THE AUTHOR'S WRITTEN PERMISSION. THE AUTHOR ATTESTS THAT PERMISSION HAS BEEN OBTAINED FOR THE USE OF ANY COPYRIGHTED MATERIAL APPEARING IN THIS THESIS (OTHER THAN BRIEF EXCERPTS REQUIRING ONLY PROPER ACKNOWLEDGEMENT IN SCHOLARLY WRITING) AND THAT ALL SUCH USE IS CLEARLY ACKNOWLEDGED. 2 ABSTRACT Feldspar group minerals are among the most abundant mineral groups in the Earth’s lithosphere and have been documented, studied and analyzed for a wide range of petrologic purposes. The methods used to examine feldspars include cathodoluminescence, petrographic examinations including Michel-Levee compositions, scanning electron microscope and electron microprobe analysis (SEM and EMP), ion microprobe and laser ablation ICP-MS analysis, studies of isotope ratios and X-Ray Diffraction (XRD). As a result the physical properties and paragenesis of feldspars are well understood, however UV fluorescence is one property which has long been described but has not been fully quantified. In this study, the fluorescence of a selected suite of feldspar group minerals was examined to investigate the link between fluorescence and crystal chemistry through determination of major and trace elements. The methods used included petrographic characterization, UV fluorescing imaging and image analysis, electron microprobe analysis, and crystal-structure modeling. Samples from Canada and the United States were used in this study focusing on compositions of the following alkali feldspars: microcline (including amazonite) and orthoclase (including adularia); and plagioclase feldspars (albite, oligoclase, labradorite, bytownite and anorthite). Features such as intercrystalline impurities were also examined. Fluorescence is generally thought to be controlled by activator elements, typically metal cations (Fe2+, Fe3+, Ti and Mn) or REEs. Electrons within these elements become excited by photons at UV wavelengths which cause electron excitation, i.e. a jump to a higher orbital. The de-excitation of this electron then causes a loss in energy that is released as light, at a different wavelength than that the photon which was originally absorbed. In the case of UV fluorescence these emitted photons are visible to the human eye. Integrating results from all of the methods show that different compositions of feldspar fluoresce with similar colors but at strongly variable intensities. Microprobe data, combined with x-ray mapping and UV imaging, showed that there was a significantly higher intensity of fluorescence in K-feldspars, while plagioclase group feldspars have a much lower intensities. Orthoclase and microcline fluoresced very strongly, albite less so, and anorthite showed the lowest fluorescence intensity. However there was a negative correlation between trace element-activator contents and fluorescence intensity. Taking crystal structure into consideration, the unit cell parameters increase in K-feldspar. This along with the monoclinic structure may allow greater photon channeling and thus increases the intensity of fluorescence. Future work employing more sensitive trace-element analysis and UV spectroscopy and XRD are recommended to fully understand the link between fluorescence and crystal chemistry. Feldspar, Fluorescence, Geochemistry, K-feldspar, Plagioclase, Ultra Violet light 3 I TABLE OF CONTENTS II TABLE OF FIGURES ....................................................................................................................... 6 III TABLE OF TABLES ........................................................................................................................ 6 ACKNOWLEDGEMENTS ................................................................................................................... 7 1.0 INTRODUCTION ......................................................................................................................... 8 1.1 General Statement ................................................................................................................ 8 1.2 Feldspar Minerals .................................................................................................................. 9 1.3 Thesis Objectives ................................................................................................................. 12 2.0 BACKGROUND KNOWLEDGE ................................................................................................... 13 2.1 Brief History of Mineral Fluorescence ................................................................................ 13 2.2 Mineral Fluorescence .......................................................................................................... 14 2.3 Fluorescence in Feldspars ................................................................................................... 17 3.0 METHODS ................................................................................................................................ 18 3.1 Data Collection .................................................................................................................... 18 3.1.1 Petrographic Description ............................................................................................. 18 3.1.2 Electron Microprobe .................................................................................................... 18 3.1.3 UV Imaging and Image Analysis ................................................................................... 20 3.1.4 Crystal Structure Modeling .......................................................................................... 20 3.2 Data Analysis ....................................................................................................................... 21 3.3 Sources of Error .................................................................................................................. 22 4.0 RESULTS ................................................................................................................................... 24 4.1 General Statement .............................................................................................................. 24 4.2 Whole Sample Analysis ....................................................................................................... 24 4.3 Petrographic Description .................................................................................................... 27 4.3.1 Sample 303 ................................................................................................................... 27 4.3.2 Sample 414 ................................................................................................................... 28 4.3.3 Sample 446 ................................................................................................................... 29 4.3.4 Sample TMB ................................................................................................................
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