|
|
 |
|||||||||||||||||
|
|||||||||||||||||
 |
|||||||||||||||||
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
CNR-Centro di Studio per la Cristallochimica e la Cristallografia (CSCC), Pavia, Italy
Single-crystal structure-refinement and electron-microprobe analysis of synthetic amphiboles with nominal fluoro-eckermannite composition and different trivalent cations (Al, Sc, Ti (super 3+) , V (super 3+) , Cr (super 3+) , Ga,) show significant deviations from nominal stoichiometry. Synthetic Sc- and Cr-bearing fluoro-eckermannite are close to nominal stoichiometry, whereas the corresponding nominal Al-, V (super 3+) -, Ga-, and Ti-bearing species contain very few trivalent cations and approximate Na(NaMg)Mg 5 Si 8 O 22 F 2 , a composition that has not been found in natural systems. The presence of a significant cummingtonite component strongly affects unit-cell parameters, coordination geometry around the B-, C-, and T-group sites, and cation ordering at the A-group sites. The high-charge cations are completely ordered at the M2 site, and there is a well-developed linear relationship between "M2-O" and the constituent-cation radius at the M2 site. The synthetic fluoro-eckermannite structure is stabilized by large spherically symmetric trivalent cations at the M2 site; for small spherically symmetric trivalent cations, it is not stable (at least at the synthesis conditions used here). Synthetic chromium-fluoro-eckermannite is stabilized by the non-spherically symmetric 3d 3 electronic arrangement, whereas Ga and V (super 3+) (3d 2 ) do not stabilize the fluoroeckermannite structure.
This record provided courtesy of AGI/GeoRef.
This article has been cited by other articles:
|
|
 |
|
  R. Oberti, G. D. Ventura, and F. Camara New Amphibole Compositions: Natural and Synthetic Reviews in Mineralogy and Geochemistry, October 1, 2007; 67(1): 89 - 124. [Full Text] [PDF]
|
|
|
|
|
|
R. Oberti, F. C. Hawthorne, E. Cannillo, and F. Camara Long-Range Order in Amphiboles Reviews in Mineralogy and Geochemistry, October 1, 2007; 67(1): 125 - 171. [Full Text] [PDF]
|
|
|
|
 |
|
 M. TIEPOLO, A. ZANETTI, R. OBERTI, R. BRUMM, S. FOLEY, and R. VANNUCCI Trace-element partitioning between synthetic potassic-richterites and silicate melts, and contrasts with the partitioning behaviour of pargasites and kaersutites European Journal of Mineralogy, April 1, 2003; 15(2): 329 - 340. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. Oberti, J. M. Caballero, L. Ottolini, S. Lopez-Andres, and V. Herreros Sodic-ferripedrizite, a new monoclinic amphibole bridging the magnesium-iron-manganese-lithium and the sodium-calcium groups American Mineralogist, March 1, 2000; 85(3-4): 578 - 585. [Abstract] [Full Text] [PDF]
|
|
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
