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American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu / Swainson, Ian


IMPACT FACTOR 2018: 2.631

CiteScore 2018: 2.55

SCImago Journal Rank (SJR) 2018: 1.355
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1945-3027
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Volume 100, Issue 5-6

Issues

Review. Routine characterization and interpretation of complex alkali feldspar intergrowths

Ian Parsons
  • Corresponding author
  • Grant Institute of Earth Science, University of Edinburgh, James Hutton Road, Edinburgh, EH9 3FE, U.K.
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/ John D. Fitz Gerald
  • Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia
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/ Martin R. Lee
  • School of Geographical and Earth Sciences, University of Glasgow, Lilybank Gardens, Glasgow, G12 8QQ, U.K.
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Published Online: 2015-05-12 | DOI: https://doi.org/10.2138/am-2015-5094

Abstract

Almost all alkali feldspar crystals contain a rich inventory of exsolution, twin, and domain microtextures that form subsequent to crystal growth and provide a record of the thermal history of the crystal and often of its involvement in replacement reactions, sometimes multiple. Microtextures strongly influence the subsequent behavior of feldspars at low temperatures during diagenesis and weathering. They are central to the retention or exchange of trace elements and of radiogenic and stable isotopes. This review is aimed at petrologists and geochemists who wish to use alkali feldspar microtextures to solve geological problems or who need to understand how microtextures influence a particular process. We suggest a systematic approach that employs methods available in most well founded laboratories. The crystallographic relationships of complex feldspar intergrowths were established by the 1970s, mainly using single-crystal X‑ray diffraction, but such methods give limited information on the spatial relationships of the different elements of the microtexture, or of the mode and chronology of their formation, which require the use of microscopy. We suggest a combination of techniques with a range of spatial resolution and strongly recommend the use of orientated sections. Sections cut parallel to the perfect (001) and (010) cleavages are the easiest to locate and most informative. Techniques described are light microscopy; scanning electron microscopy using both backscattered and secondary electrons, including the use of surfaces etched in the laboratory; electron-probe microanalysis and analysis by energy-dispersive spectrometry in a scanning electron microscope; transmission electron microscopy. We discuss the use of cathodoluminescence as an auxiliary technique, but do not recommend electron-backscattered diffraction for feldspar work. We review recent publications that provide examples of the need for great care and attention to pre-existing work in microtextural studies, and suggest several topics for future work.

Keywords: Chemical diffusion; diffraction; fluids in the crust (special collection); mineral physics; nanoscale

About the article

Received: 2014-06-13

Accepted: 2014-11-08

Published Online: 2015-05-12

Published in Print: 2015-05-01


Citation Information: American Mineralogist, Volume 100, Issue 5-6, Pages 1277–1303, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am-2015-5094.

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© 2015 by Walter de Gruyter Berlin/Boston. This work is licensed under the MSA License. (view license)

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