Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Reguir, E. P. Articles by Mitchell, R. H. Search for Related Content GeoRef GeoRef Citation

Pb-bearing hollandite-type titanates: A first natural occurrence and reconnaissance synthesis study

¹ Department of Geological Sciences, University of Manitoba, 125 Dysart Road, Winnipeg, Manitoba, R3T 2N2, Canada
² epartment of Geology, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario, P7B 5E1, Canada

^* E-mail: chakhmou{at}ms.umanitoba.ca

Some samples of hollandite-type titanates from the Murun alkaline complex (Yakutia, Russia) contain appreciable amounts of Pb (up to 12.5 wt.% PbO). These titanates occur in a pegmatitic K-feldspar-aegirine rock containing subordinate K-rich batisite, titanite, wadeite and other minerals. The Pb-bearing crystals coexist with hollandite-type phases devoid of detectable Pb and zoned from a K-dominant (priderite) core to a Ba-dominant (henrymeyerite) rim. Recalculation of the microprobe analyses on the stoichiometric basis indicates that most of the Fe occurs in this mineral in trivalent form, suggesting the existence of a solid solution between the Ba(Ti₆Fe₂³⁺)O₁₆, K₂(Ti₆Fe₂³⁺)O₁₆ and Pb(Ti₆Fe₂³⁺)O₁₆ end-members. The maximum proportion of the latter end-member in the Murun titanates is ~45 mol.%. The Ba-free compositions [Pb_1.0–1.3(Ti,Fe)₈O₁₆] and intermediate members of the (Ba_1–xPb_x)(Ti₆Fe₂³⁺)O₁₆ series were synthesized at 1050–1100°C. The synthesis products comprise tetragonal hollandites of various stoichiometry intermixed with rutile, a pseudobrookite-type phase and (for the Ba-free compositions) minor macedonite. Electron microprobe analyses of the hollandites indicate that there is a continuous series of compositions between the two hexatitanate end-members, Ba(Ti₆Fe₂³⁺)O₁₆ and Pb(Ti₆Fe₂³⁺)O₁₆. The crystal structure of one intermediate member was refined by the Rietveld method in space group I4/m, and found to differ from the hollandite archetype (i.e. Pb-bearing Ba manganate) in that Pb is preferentially partitioned into the 2b tunnel site at (0,0,), whereas Ba is partitioned into the larger 4e site at (0,0,~0.8).

KEYWORDS: hollandite, cryptomelane group, titanate, alkaline pegmatite, Murun complex, Yakutia, synthesis, structure, cation ordering

This article has been cited by other articles:

				M. Pasero A Short Outline of the Tunnel Oxides Reviews in Mineralogy and Geochemistry, January 1, 2005; 57(1): 291 - 305. [Full Text] [PDF]