|
|
 |
|||||||||||||||||
|
|||||||||||||||||
 |
|||||||||||||||||
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Letter |
1 Department of Earth and Environment, Mount Holyoke College, South Hadley, Massachusetts 01075, U.S.A.
2 Department of Geological Sciences, University of Idaho, Moscow, Idaho 83844, U.S.A.
3 Department of Geological Sciences, Rutgers University, Piscataway, New Jersey 08854, U.S.A.
4 GSECARS and Department of Geophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637, U.S.A.
Correspondence: * E-mail: mddyar{at}mtholyoke.edu
A new method has been developed to orient 50–100 µm size single crystals to obtain XANES or EXAFS spectra along any crystallographic orientation relative to a polarized synchrotron X-ray beam. The method uses a modified spindle stage and an X-ray goniometer head to hold a crystal and the glass fiber on which it is mounted. The orientation of the crystallographic axes within the crystal can be determined by X-ray diffraction in all cases or with the use of the polarizing light microscope if the minerals are biaxial. Once an optical orientation direction has been located, it can be oriented parallel to the polarization direction of the synchrotron source for spectral acquisition.
Mineral samples representing the three optical classes (i.e., isotropic, uniaxial, and biaxial) were oriented along their a, b, and c crystallographic axes, and Fe-XANES spectra were obtained. In all cases the interactions of polarized X-rays with the crystal structures are analogous to the interactions of visible light (e.g., as represented by refractive index). For the isotropic almandine sample the XANES spectra were similar at all orientations. For the uniaxial buergerite and scapolite samples the spectra were similar along the a and b axes and different along c. A detailed set of spectra acquired at multiple (known) optical orientations in the scapolite crystal demonstrates that spectral features vary in intensity as a function of orientation, with maxima and minima when the X-rays are polarized along optical orientations. For the biaxial fayalite sample, the XANES spectra differed along all three crystallographic axes, as expected by analogy to optical properties.
This article has been cited by other articles:
|
|
 |
|
  M. Andreani, O. Grauby, A. Baronnet, and M. Munoz Occurrence, composition and growth of polyhedral serpentine European Journal of Mineralogy, April 1, 2008; 20(2): 159 - 171. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. Cibin, G. Cinque, A. Marcelli, A. Mottana, and R. Sassi The octahedral sheet of metamorphic 2M1-phengites: A combined EMPA and AXANES study American Mineralogist, February 1, 2008; 93(2-3): 414 - 425. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. Cibin, A. Mottana, A. Marcelli, and M. F. Brigatti Angular dependence of potassium K-edge XANES spectra of trioctahedral micas: Significance for the determination of the local structure and electronic behavior of the interlayer site American Mineralogist, July 1, 2006; 91(7): 1150 - 1162. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. E. Gunter, R. T. Downs, K. L. Bartelmehs, S. H. Evans, C. J.S. Pommier, J. S. Grow, M. S. Sanchez, and F. D. Bloss Optic properties of centimeter-sized crystals determined in air with the spindle stage using EXCALIBRW American Mineralogist, October 1, 2005; 90(10): 1648 - 1654. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. D. Dyar, M. E. Gunter, J. S. Delaney, A. Lanzarotti, and S. R. Sutton SYSTEMATICS IN THE STRUCTURE AND XANES SPECTRA OF PYROXENES, AMPHIBOLES, AND MICAS AS DERIVED FROM ORIENTED SINGLE CRYSTALS Can Mineral, October 1, 2002; 40(5): 1375 - 1393. [Abstract] [Full Text] [PDF]
|
|
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
