Computer Science
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.524i&link_type=abstract
Meteoritics, vol. 30, no. 5, page 524
Computer Science
Breccia, Meteoritic, Chondrites, Heideite, Meteorites, Bustee, Kaidun
Scientific paper
The Kaidun meteorite is an unique breccia that contains a set of different types of carbonaceous and enstatite chondrite clasts as well as an enstatite achondrite-like clast [1, 2]. Kaidun also contains some rare and new minerals, e.g. Ti-Fe and Cr-Fe phosphides [3]. Here we present the results of a study of Ti-Fe-S-bearing compounds which were found in the polished section of the fragment #53.09. The main part of the fragment is a carbonaceous C1-2 breccia that also contains large grains of enstatite, forsterite, and olivines. Grain of metal (Si<0.1 wt.%) also present. No opaque minerals that can be apparently connected with E meteorites were found in the section. Ti-Fe-S-bearing compounds are present as rare, discrete, anhedral grains up to 50 micrometers in maximum dimension. The grains have a stripped structure and consist of subparallel thin (up to a few micrometers) light (LB) and dark (DB) bars. IDX data show a high oxygen content in DB and only a small oxygen content in LB. The compositions of LB and DB are variable; the representative compositions (average of 4 analyses for each, wt.%) are presented below in elementary (LB) and oxidized (DB) forms in accordance with IDX data. LB: S 36.7, Ti 33.7, Cr 2.0, Fe 14.7, Mg 0.1, Na 0.3, total 87.8. DB: SO3 36.9, TiO2 41.6, Cr2O3 2.4, FeO 14.7, MgO 1.7, Na2O 1.1, total 98.4. Taking into consideration the stripped structure of the grains and IDX data, we consider the LB a mixture of a certain sulfide and DB. The composition of a sulfide after subtraction of DB admixture (S 45.3, Ti 36.7, Cr 2.2, Fe 16.0) can be approximated by the formula (Fe,Cr)0.93Ti2.17S4. It is very close to the formula of heideite (Fe,Cr)1+x(Ti,Fe)2S4, the only Ti-Fe sulfide known to date, found in the Bustee aubrite [4]. Thus this is the second finding of heideite in nature. We consider the DB to be a product of aqueous alteration of heideite. The similar Ti/Cr ratio in heideite and in the its alteration product (16.7 and 15.6 correspondingly) may indicate that the alteration was accompanied by removal of S and Fe while Ti and Cr were stable in the process. The stripped structure of the partly altered grains may be mainly connected with a peculiarity of the primary structure of heideite. The discovery of heideite in the Kaidun complex breccia does not appear to clarify the genesis of this mineral, which is also unclear from the thermodynamic point of view [5]. This study was supported partly by RFFI Grant 95-05-14547. References: [1] Ivanov A. V. (1989) Geochem. Intern., 26, 84-91. [2] Clayton R. N. et al. (1994) LPS XXV, 269-270. [3] Ivanov A. V. et al. (1994) LPS XXV, 595-596. [4] Keil K. and Brett R. (1974) Am. Mineral., 59, 465-470. [5] Petaev M. I. et al. (1987) Geochimiya, 64-75, in Russian.
Ivanov Alexei V.
Kononkova Natal'ia N.
MacPherson Glenn J.
Stroganov I. A.
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