In Iron Silicide

CALCIUM-ALUMINUM-RICH INCLUSIONS (CAIs) IN IRON SILICIDE (XIFENGITE, GUPEIITE, HAPKEITE) 76th Annual Meteoritical Society Meeting (2013) MATTER: EVIDENCE OF A COSMIC ORIGIN 5055.pdf Abstract The CAIs Mm- to cm-sized metallic particles in the subsoil of -- The iron silicides from the Chiemgau impact strewn field contain CAIs with M.A. Rappenglück the Alpine Foreland are composed of iron silicides minerals CaAl2O4, calcium monoaluminate, and Ca2Al2O5, dicalcium dialuminate. Institute for Interdisciplinary Studies, Fe3Si, mineral gupeiite, Fe5Si3, mineral xifengite, -- The monoclinic high-temperature (>1,500°C), low-pressure dimorph of CaAl2O4, Gilching, Germany, [email protected] Fe2Si, mineral hapkeite, FeSi, fersilicite, and FeSi2, mineral krotite, was first identified in a CAI from the CH chondrite NWA 470 [17] ferdisilicite, the minerals gupeiite, xifengite and and later reported [18, 19] to exist in a CAI in the carbonaceous chondrite meteorite F. Bauer 10 µm 2 µm NWA 1934. fersilicite being the main components. More peculiar Oxford Instruments GmbH Nano- Science, mineral components add to the matrix also hosting -- The orthorhombic Ca2Al2O5 dicalcium dialuminate high pressure phase with the Fig. 6. Zircon crystals obviously having impacted larger crystals of extremely pure titanium carbide, Fig. 5. Zircon crystals in iron silicide matrix. brownmillerite-type structure was established in 2000 [20] and has so far no natural Wiesbaden Germany, The white tips on the crystals have been shown a plastic or liquid iron silicide matrix that seems [email protected] mineral khamrabaevite, and silicon carbide, mineral to be uranium. to have been frozen during the disturbance. counterpart. Experimental data were 1,250°C and 2.5 GPa, and stability was reached moissanite. Intriguing components are CAIs proved between 4 and 9 GPa and at ≈ 1,500 K. to be Ca2Al2O5 (dicalcium aluminate) and the 10 µm M. Hiltl calcium aluminate CaAl2O4. This strange cocktail, Fig. 17. The CAIs (stronger Carl Zeiss Microscopy GmbH, Oberkochen, magnification in Fig. 18) have evidence of shock effects, and last but not least the Fig. 1. Location map for the Germany find situations of the particles speak in favor of a finds of the iron silicides. been established in this typical texture of many iron silicide [email protected] meteoritic origin of the iron silicide pieces and particles: titanium carbide suggest a relation to the Holocene large Chiemgau (dark gray) and silicon carbide impact event. (moissanite, black) crystals in Andreas Neumair a matrix of intergrowth of various iron silicide minerals Institute for Interdisciplinary Studies, Introduction 100 µm (gupeite, xifengite, hapkeite, Gilching, Germany, -- Iron silicides have been playing a major role in the discovery and discussion fersilicite, ferdisilicite). Fig. 7. Zirconium (zircon or/and baddeleyite) Fig. 8. Peculiar ornate structures in the iron [email protected] of the Holocene large Chiemgau meteorite impact event [1-15]. possible exsolution lamellae in iron silicide. silicide matrix lacking a conclusive explanation. -- They were detected by local history researchers in the Alpine Foreland Possibly spotty melting of the matrix. (Southeast Germany, Fig. 1) in the subsoil down to the substratum. Kord Ernstson -- The ironsilicides proved to be ferrosilicides Fe3Si, mineral gupeiite, and Faculty of Philosophy I, University of Fe5Si3, mineral xifengite. The ferrosilicides regularly occurred near rimmed Würzburg, Würzburg, Germany, craters. [email protected] -- Early conclusion: Both the strange matter and the craters could perhaps be related with a meteorite impact in historical time, especially with regard to strongly restricted terrestrial formation of gupeiite and xifengite and their occurrences in cosmogenic globular particles from the Yanshan area in China The CAI cosmic relevance [16]. Opponents and critics of the Chiemgau impact per se 1 mm 20 µm I -- An industrial origin was considered because the iron silicides had been CA don't grow tired of pointing to an industrial byproduct of produced in the local industry as a completely unknown byproduct. Fig. 9. Multiple sets of subparallel, mostly Fig. 10. Strongly fractured titanium carbide crystal the iron silicides [23]. They ignore: -- An industrial production could largely be excluded because of many find open fractures in iron silicide matrix. in iron silicide matrix. Note the open, tensile 100 µm situations absolutely incompatible with anthropogenic support. fractures pointing to dynamic (shock?) spallation -- Iron silicides occur in the most reduced meteorites. -- Here, we report on completely new analyses of these iron silicide particles fracturing. Fig. 18. Iron silicide matrix (light gray) with inclusions of TiC -- Cubic moissanite and titanium carbide exist in some (dark gray), moissanite SiC with black C (graphite, diamond?) from different locations using various SEM and TEM techniques. They show 100 µm meteorites and have been verified in cosmic dust. 20 µm film and light edging CAIs. the industrial hypothesis can be ruled out with a high degree of probability, and Silicon and titanium carbides [SiC,moissanite, -- On earth, the hapkeite, Fe2Si iron silicide (in its cubic they suggest a cosmic, extraterrestrial origin. form) is known from the Dhofar 280 lunar fragmental (Ti,V,Fe)C khamrabaevite] Discussion and relations breccia meteorite [24] and has been reported for magnetic The material (Fig. 2) -- A significant feature of all analyzed iron silicide particles is their content of spherules in Hungary that are ascribed to cosmic dust or The Chiemgau impact and meteorite crater strewn field meteorite impact [25]. A grain similar in composition to -- The mass of iron silicides so far sampled in the region totals roughly 2 kg. titanium and silicon carbides. They occur as extremely pure crystals and more finely dispersed in the matrix. hapkeite occurs in the FRO 90228 ureilite [26], and Fe2Si, -- The size of the particles ranges between the order of a millimeter and a few -- The Chiemgau strewn + eld [3, and centimeters. The largest piece is 6 cm long and has a mass of 162 g. --The SiC has been analyzed to be the cubic moissanite mineral – (b)3C-SiC. together with TiC and supernova material, was established references therein] comprises more than in the Orgueil meteorite [27]. -- Some of the particles exhibit a spherical or ellipsoidal shape, but often a --The titanium carbide in general occurs as the (Ti,V,Fe)C mineral khamrabaevite, 80 mostly rimmed craters scattered in a convex smooth front combines with a flat irregularly shaped rear side. and also the off-stoichiometric form of TiC0.63 has been shown to exist. region of about 60 km length and ca. 30 Now, apart from the strong evidence for shock processes, -- The surfaces show metallic luster and lack practically any corrosion. -- Moissanite crystals may show multiple sets of planar features reminding of km width in the very South-East of the established CAIs add to the cosmic component of the -- In many cases, a regmaglyptic surface resembling ablation features of shock-produced planar deformation features (PDFs) known from various minerals. Germany (Fig. 16, Fig. 1). Chiemgau iron silicides. CAIs are a mineralogically and meteorites is striking. -- The crater diameters range between a chemically diverse group of structures mainly known -- Frequently, sparkling crystals can be seen with the naked eye to stick out few meters and a few hundred meters, from carbonaceous chondrites. They consist of various among them Lake Tüttensee, the hitherto minerals that formed from a high temperature gas at early from the metallic matrix. established largest crater of the strewn +eld with a rim-to-rim diameter of about stages of the Solar System formations. 2 cm B 600 m and an extensive ejecta blanket. -- Geologically, the craters occur in For the krotite the conditions of high temperature and low Fig. 16. Location map of the Chiemgau Pleistocene moraine and f uvio-glacial pressure are consistent with a hypothesis that the mineral impact elliptically shaped strewn field (see sediments. found in the NWA 1934 meteorite formed as high- millimeter Fig. 1). scales temperature condensate from the solar nebula. -- The impact is substantiated by [3, and references therein] 100 µm heavy deformations of the Quaternary cobbles and boulders in and Conclusions A around the craters abundant fused rock material (impact melt rocks and various glasses) For the iron silicide particles the intimate CAI coexistence D Fig. 11. Cubic moissanite crystals sticking Fig. 12. Titanium carbide crystals in the matrix of of the high-temperature/low-pressure CaAl O krotite and out from the iron silicide matrix occur. 2 4 intergrowth of FeSi, gupeiite and xifengite iron shock-metamorphic effects (planar deformation features, PDFs, the high-pressure Ca Al O phase imply a complex silicides. 2 2 5 diaplectic glass) formation history. In addition to the many other peculiar geophysical anomalies properties (xifengite, gupeiite, hapkeite, fersilicite, abundant occurrence of metallic, glass and carbon spherules, ferdisilicte intergrowth, extremely pure, in part larger accretionary lapilli high-pressure/high-temperature carbon allotropes [7, 13]. crystals of cubic moissanite and khamrabaevite, various C indications of probable shock effects) featured by the iron 1.5 cm -- The impactor is suggested to have been a roughly 1,000 m sized low- density disintegrated, loosely bound asteroid or a disintegrated comet in silicides

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