New typology and origin of tsavorite based on trace-element chemistry

Research areas:

• Surfaces planétaires (2011 - 2016)

Year:

2014

Authors:

• Julien Feneyrol
• Gaston Giuliani
• Daniel Ohnenstetter
• Benjamin Rondeau
• Emmanuel Fritsch
• Anthony E. Fallick
• Daniel Ichang'
• i
• Edward Omito
• Michel Rakotondrazafy
• Madison Ranatsenho
• Florent Lallier

Journal:

EUROPEAN JOURNAL OF MINERALOGY

Volume:

26

Number:

2

Pages:

293-308

Month:

March

ISSN:

0935-1221

BibTex:

@article{WOS:000334918100009, author = "Julien Feneyrol and Gaston Giuliani and Daniel Ohnenstetter and Benjamin Rondeau and Emmanuel Fritsch and Anthony E. Fallick and Daniel Ichang{\&}#039 and i and Edward Omito and Michel Rakotondrazafy and Madison Ranatsenho and Florent Lallier", abstract = "New electron-microprobe analyses of `tsavorites{\&}#039; 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 {\&}gt; Cr {\&}gt; Mn (in atoms per formula unit); type 2, vanadian grossular with V {\&}gt; Mn {\&}gt; Cr; type 3, Mn-bearing vanadian grossular with Mn {\&}gt; V {\&}gt; Cr; type 4, Mn-bearing chromian grossular with Mn {\&}gt; Cr {\&}gt; V; and type 5, Cr- and Mn-bearing grossular with Cr {\&}gt; Mn {\&}gt; 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{{\&}#039;{\&}#039;} for determining the geographic provenance of economic tsavorite from Kenya, Tanzania and Madagascar.", doi = "10.1127/0935-1221/2014/0026-2367", extra = "PICL", issn = "0935-1221", journal = "EUROPEAN JOURNAL OF MINERALOGY", month = "MAR", number = "2", pages = "293-308", title = "{N}ew typology and origin of tsavorite based on trace-element chemistry", volume = "26", year = "2014", }

Abstract:

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.