Abstract
Rare type of silicate inclusions found in the Elga iron meteorite (group IIE) has a very specific mineral composition and shows silicate (≈90%)–natrophosphate (≈10%) liquid immiscibility due to meniscus-like isolation of Na-Ca-Mg-Fe phosphates. The 3 mm wide immiscible inclusion has been first studied in detail using optical microscopy, scanning electron microscopy, electron microprobe analysis and Raman spectroscopy. The silicate part of the inclusion contains fine-grained quartz-feldspar aggregate and mafic minerals. The relationships of feldspars indicate solid decay of initially homogenous K-Na-feldspar into albite and K-feldspar with decreasing of temperature. Some mafic minerals in the silicate part are exotic in composition: the dominant phase is an obertiite-subgroup oxyamphibole (amphibole supergroup), varying from ferri-obertiite NaNa2Mg3Fe3+Ti[Si8O22]O2 to hypothetical NaNa2Mg3Fe2+0.5Ti1.5[Si8O22]O2; minor phases are the aenigmatite-subgroup mineral (sapphirine supergroup) with composition close to median value of the Na2Fe2+5TiSi6O18O2-Na2Mg5TiSi6O18O2 join, orthopyroxene (enstatite), clinopyroxene of the diopside Ca(Mg,Fe)Si2O6–kosmochlor NaCrSi2O6-Na(Mg,Fe)0.5Ti0.5Si2O6 series and chromite. The alteration phases are represented by Fe-dominant chlorite, goethite and hydrated Na2O-rich (2.3–3.3 wt.%) Fe-phosphate close to vivianite. Natrophosphate part consists of aggregate of three orthophosphates (brianite, czochralskiite, marićite) and minor Na-Cr-Ti-clinopyroxene, pentlandite, rarely taenite. Czochralskiite Na4Ca3Mg(PO4)4 is rich in FeO (2.3–5.1 wt.%) and MnO (0.4–1.5 wt.%). Brianite Na2CaMg(PO4)2 contains FeO (3.0–4.3 wt.%) and MnO (0.3–0.7 wt.%) and marićite NaFe(PO4) bears MnO (5.5–6.2 wt.%), MgO (5.3–6.2 wt.%) and CaO (0.5–1.5 wt.%). The contact between immiscible parts is decorated by enstatite zone in the silicate part and diopside–kosmochlor clinopyroxene zone in the natrophosphate ones. The mineralogy of the studied immiscible inclusion outlines three potentially new mineral species, which were first identified in meteorites: obertiite–related oxyamphibole NaNa2Mg3Fe2+0.5Ti1.5[Si8O22]O2, Mg-analog of aenigmatite Na2Mg5TiSi6O18O2 and Na-Ti-rich clinopyroxene Na(Mg,Fe)0.5Ti0.5Si2O6.
Highlights
This publication provides a detailed description of the mineralogy for an Elga silicate inclusion with silicate-natrophosphate immiscibility
Raman spectroscopy does not give any direct information about structural state of K-feldspar (Figure S14)
It is assumed that IIE irons have genetic relations to H-chondrite-like bodies according to isotopic and geochemical characteristics [68,69,70,71]
Summary
The Elga iron meteorite (group IIE) is a fine-grained octahedrite with up to 15 vol.% silicate inclusions and with local zones of shock metamorphism [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]. Silicate-bearing iron meteorites represent about 4% of all iron meteorites. They are important for understanding metal-silicate partitioning in processes related to the formation and evolution of asteroids and terrestrial planets. IVA (5%); silicate inclusions were inclusions were reported for 8 ungrouped iron meteorites [15]. The mineralogy inclusions inclusions the peculiarities of metal-silicate relations of in silicate meteorite parentalindicates bodies. The peculiarities of metal-silicate relations in meteorite parental bodies. The exotic mineral composition exotic mineral composition of some silicate inclusions may reflect local specific conditions within of some silicate may reflect local specific conditions withininclusion parental with bodies.
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