Unusual large chromite crystals in the Saint Aubin iron meteorite

Abstract

Abstract-In the Saint Aubin octahedrite, chromite crystals of up to 3 cm occur enclosed in the metal phase. They are twinned along [111] according to the spinel law and display pseudohexagonal shapes in cross-sections. The crystals are homogeneous and exhibit compositions close to pure chromite endmember. Vanadium is the only additional element observed in appreciable amounts of up to 0.73 wt%. Chromite in the Saint Aubin meteorite crystallized from liquids with very low amounts of Cr and O close to the Fe-FeS join as indicated by its composition and phase relations. The growth of large chromite crystals implies stable supersaturated conditions for a long period in the meteorite parent body of Saint Aubin.

Noble gas content and isotope abundances in phases of the Saint‐Aubin (UNGR) iron meteorite

“…5). The reason for the large variation is probably due to the fact that SaintAubin chromite is mostly pure Fe-chromite (Fehr and Carion 2004;Kurat et al 2005), and because the target elements to produce the cosmogenic or the fissiogenic Kr and Xe (for example, Mo, Ru, Ir, Pt, Au, etc.) are present in very small amounts and are possibly inhomogeneously distributed.…”

“…It is an octahedrite with a fine (0.4 mm) Widmanstätten pattern and is chemically classified as an ungrouped iron (Dransart and Baron 2003). Saint-Aubin contains a variety of inclusions: iron phosphate (sarcopside or graftonite), sulfide, needles of schreibersite up to 10 cm in length, and giant euhedral chromite of ~3 cm in size (Fehr and Carion 2004;Kurat et al 2005).…”

“…Thus the large size of the chromite in Saint-Aubin is very unusual. Saint-Aubin is regarded as a magmatic iron meteorite because the composition of the chromite inclusion is similar to pure FeCr 2 O 4 and slow cooling would be required to produce such a pure chromite (Ulff-Møller 1998;Fehr and Carion 2004). Furthermore, Kurat et al (2005) determined the major, minor and trace element contents of the chromite and found that it is very poor in lithophile and siderophile elements (only ~600 ppm Mg, 0.4 ppm Al, 1.8 ppm Ni), Sc and REE.…”

Zincian chromite inclusions in diamonds: Possibility of deep recycling origin

“…Chromites have been found in iron meteorites (Bunch et al, 1970;Bunch and Keil, 1971;Wasson et al, 1999;Fehr and Carion, 2004), stony iron meteorites (Wasson et al, 1999), and achondrites (Chikami et al, 1999). Some of them contain appreciable amounts of Zn (e.g., Bunch et al, 1970;Chikami et al, 1999).…”

“…The plots also show chromites low in Zn and Mn and associated with zincian chromites for altered/metamorphosed rocks. Data sources are as follows: Meyer and Boyd (1972), Stachel et al (2000), Taylor et al (2003), and Donnelly et al (2007) for diamond inclusions; Bunch et al (1970Bunch et al ( , 1972, Bunch and Keil (1971), Desnoyers et al (1985), Krot et al (1992), Ikeda et al (1997), Chikami et al (1999), Wasson et al (1999), and Fehr and Carion (2004) for meteorites; and Thayer et al (1964), Wylie et al (1987), Challis et al (1995), Weiser and Hirdes (1997), Gahlan and Arai (2007), and Johan and Ohnenstetter (2010) for low -temperature altered/metamorphosed peridotites and related rocks. Zincian chromite of possible deep recycling origin Relationships between Cr/(Cr + Al) atomic ratio and Mg#, and Cr -Al -Fe 3+ atomic ratios of zincian chromites and related spinels.…”