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Hidden story of tapiolite

Published online by Cambridge University Press:  05 July 2018

T. S. Ercit
T. S. Ercit*
Affiliation:
Canadian Museum of Nature, P.O. Box 3443, Station “D”, Ottawa, Canada K1P 6P4
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Abstract

The crystal chemistry of tapiolite is more complicated than previously recognized. Perusal and synthesis of relatively recent publications reveals a ‘hidden’ story about tapiolite, one that: (1) permits quantification of the effects of Mn, Fe3+, Ti (and Sn) upon the unit-cell parameters of maximally ordered tapiolite; (2) shows that the effect of Nb = Ta substitution upon unit-cell parameters is insignificant; (3) casts doubt on the usefulness of heating experiments for accurately evaluating cation order in tapiolite; (4) suggests that rutile exsolves from tapiolite upon heating in air at lower temperatures than previously established; (5) shows that the maximum solubility of TiO2 in FeTa2O6 tapiolite during the later stages of crystallization of granitic pegmatites is ∼1 mol.%; (6) shows that the heating paths for at least some natural tapiolite samples are not necessarily linear, consisting of two sequential steps; (7) sheds doubt on the usefulness of unit-cell parameters as quantitative measures of long-range cation order, Q, in tapiolite; but (8) does show that the intensity ratio I011/I110 can provide an accurate and reasonably precise measure of cation order in tapiolite.

Keywords

tapioliteorder-disordersolid solutiongranitic pegmatites
Type
Research Article
Information
Mineralogical Magazine , Volume 74 , Issue 4 , August 2010 , pp. 715 - 730
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2010

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