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American Mineralogist

Journal of Earth and Planetary Materials

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


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1945-3027
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Volume 102, Issue 10

Issues

Protoenstatite: A new mineral in Oregon sunstones with “watermelon” colors

Huifang Xu
  • Corresponding author
  • NASA Astrobiology Institute, Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin 53706, U.S.A.
  • Email
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
/ Tina R. Hill
  • NASA Astrobiology Institute, Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin 53706, U.S.A.
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
/ Hiromi Konishi
  • NASA Astrobiology Institute, Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin 53706, U.S.A.
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/ Gabriela Farfan
Published Online: 2017-10-02 | DOI: https://doi.org/10.2138/am-2017-6186

Abstract

Al-Fe-bearing protoenstatite was discovered in Oregon sunstones with unusual pleochroic/dichroic red to green coloration using high-resolution transmission electron microscopy (HRTEM) and X-ray energy-dispersive spectroscopy (EDS). The empirical formula calculated on the basis of 6 O apfu is (Mg1.17Fe0.43Al0.26Ca0.03Na0.10Ti0.01)Σ2.00(Si1.83Al0.17)Σ2.00O6. The protoenstatite has a space group of Pbcn; its unit-cell parameters refined from selected-area electron diffraction patterns are a = 9.25(1), b = 8.78(1), and c = 5.32(1) Å. Protoenstatite nanocrystals are quenchable to low temperature. The crystallographically oriented nanocrystals of protoenstatite and clinoenstatite in association with copper nanocrystals are responsible for the unusual green and “watermelon” coloration of the labradorite gemstone.

Keywords: Oregon sunstone; labradorite; new pyroxene; clinoenstatite; protoenstatite; HRTEM; native copper; dichroic; Nanominerals and Mineral Nanoparticles

Special collection papers can be found online at http://www.minsocam.org/MSA/AmMin/special-collections.html.

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About the article


Received: 2017-05-09

Accepted: 2017-06-29

Published Online: 2017-10-02

Published in Print: 2017-10-26


Citation Information: American Mineralogist, Volume 102, Issue 10, Pages 2146–2149, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am-2017-6186.

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© 2017 by Walter de Gruyter Berlin/Boston.

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