%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Feneyrol, J.
%A Giuliani, Gaston
%A Ohnenstetter, D.
%A Rondeau, B.
%A Fritsch, E.
%A Fallick, A. E.
%A Ichang'i, D.
%A Omito, E.
%A Rakotondrazafy, M.
%A Ranatsenho, M.
%A Lallier, F.
%T New typology and origin of tsavorite based on trace-element chemistry
%D 2014
%L fdi:010062020
%G ENG
%J European Journal of Mineralogy
%@ 0935-1221
%K tsavorite ; green grossular ; electron microprobe analysis ; UV-Vis-NIR ; absorption spectra ; chemical typology ; V/Cr ratio ; garnet ; geographic origin ; gemmology
%K AFRIQUE DE L'EST ; KENYA ; TANZANIE ; MADAGASCAR
%M ISI:000334918100009
%N 2
%P 293-308
%R 10.1127/0935-1221/2014/0026-2367
%U https://www.documentation.ird.fr/hor/fdi:010062020
%> https://www.documentation.ird.fr/intranet/publi/2014/06/010062020.pdf
%V 26
%W Horizon (IRD)
%X New electron-microprobe analyses of 'tsavorites' from the Neoproterozoic Metamorphic Mozambique Belt deposits allow the characterization of green grossular according to its trace-element chemistry (V, Cr, Mn). Five chemical types are defined: type 1, vanadian grossular with V > Cr > Mn (in atoms per formula unit); type 2, vanadian grossular with V > Mn > Cr; type 3, Mn-bearing vanadian grossular with Mn > V > Cr; type 4, Mn-bearing chromian grossular with Mn > Cr > V; and type 5, Cr- and Mn-bearing grossular with Cr > Mn > V. These types are also characterized by different absorption spectra in the ultraviolet-visible-near infrared. Type 1 tsavorite spectra show a total absorption below 430 nm due to the high vanadium contents. Type 2 tsavorite spectra present the classical absorption bands of V. Types 3 and 4 tsavorite spectra display additional shoulders at 407 and 408 nm due to Mn2+, whereas spectra of Cr-bearing types 4 and 5 tsavorite show the two additional bands of Cr3+ at 697 and 701 nm. The different absorption spectra also indicate Fe2+-Ti4+ charge transfer. We measured OH equivalent to 0.08 to 0.38 wt% eq. H2O within the structure. Concentrations of vanadium, chromium and manganese are good chemical "fingerprints" for determining the geographic provenance of economic tsavorite from Kenya, Tanzania and Madagascar.
%$ 064