Short-range order in minerals; amphiboles

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doi: 10.2113/gscanmin.43.6.1895
Authors:Hawthorne, F. C.; Della Ventura, G.; Oberti, R.; Robert, J. L.; Iezzi, G.
Author Affiliations:Primary:
University of Manitoba, Department of Geological Sciences, Winnipeg, MB, Canada
Other:
Universita di Roma Tre, Italy
CNR, France
ISTO, Italy
Volume Title:Mineralogical Association of Canada 50th anniversary symposium volume
Volume Authors:Hawthorne, F. C., prefacer
Source:The Canadian Mineralogist, Vol.43(Part 6), p.1895-1920; The Mineralogical Association of Canada 50th anniversary symposium, Halifax, NS, May 15-18, 2005, prefaced by F. C. Hawthorne. Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada. ISSN: 0008-4476
Publication Date:2005
Note:In English. 80 refs.; illus., incl. 4 tables
Summary:Short-range order involves local clusters of atoms that occur either more or less frequently than predicted by a random distribution. IR spectroscopy in the principal OH-stretching region of amphiboles is sensitive to such local arrangements, and hence the OH group can be used as a local probe of short-range arrangements of atoms. Monoclinic amphibole in the systems richterite-pargasite, tremolite-pargasite and tremolite-hornblende show strong short-range order involving T-, C- and A-group cations. Amphiboles involving OH-F solid solution with [] (vacancy) at the A site (e.g. tremolite-fluorotremolite) show one-mode behaviour, whereas amphiboles with Na or K at the A site (e.g. richterite-fluororichterite) show two-mode behaviour, indicating that nearest-neighbour arrangements of atoms couple through an occupied A site, but do not couple through a vacant A site. The relative band intensities in OH-F amphibole solid solutions showing two-mode behaviour indicate that OH and F are completely short-range disordered with respect to each other. Amphiboles in the system pargasite-fluoropargasite show strong short-range disorder of OH and F with regard to the cations occupying the associated nearest-neighbour M(1)M(1)M(3) sites; arrangements involving MgMgAl-OH are far more common than arrangements involving MgMgAl-F. Examination of Ti-bearing richteritic amphiboles show that [4]Ti4+ and Si are short-range disordered with regard to each other. Crystal-structure refinement, SIMS analysis and local bond-valence requirements suggest that [4]Ti4+ and O(3)O2- are locally associated at adjacent M(1) and O(3) sites. Short-range order is of significance in that it will affect the stability of amphiboles through its entropy (and enthalpy) effects. [R.A.H.]
Sections:Crystal structure; Mineral data
Mineral Groups:Double-chain silicates
Subjects:Amphibole group; Bonding; Chain silicates; Clinoamphibole; Crystal chemistry; Crystal structure; Hornblende; Hydroxyl ion; Infrared spectra; Metals; Order-disorder; Pargasite; Richterite; Silicates; Spectra; Titanium; Tremolite; Valency
Abstract Numbers:06M/1514
Record ID:2007018176
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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