On the occurrences and formation mechanisms of cliftonites: the case of Campo del Cielo iron meteorite

GARCÍA, L.N.; SHEN, P.; QUIRICO, E.; VARELA, M.E.; MONTAGNAC, G.; TOLLEY, A.; STEFANESCU, D.M.; BARUJ, A.

CARBON

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2023 vol. 208 p. 60 - 71

0008-6223

The purpose of this research is to reassess the nucleation and growth mechanism ofcliftonites, a graphite aggregate that has been reported in meteorites and terrestrialcomplexes. For this aim, their occurrence in a sample of the Campo del Cielo ironmeteorite was explored through optical and electron microscopy, and Ramanspectroscopy. This combination allowed the authors to reveal the spherulitic textures anddiversified occurrences of cliftonitic graphite, and propose them as pseudomorphs afterthe host crystal with preferred low-energy surfaces for favorable overlain extension ofgraphite basal layers. These graphite flakes assemblies with rough/flat edgesapproximately parallelly stacked as well as spherulitic sectors, would be the result ofpartial melting and solidification with grain/phase junctions and dislocations proposed asfavorable partial melting sites, under diversified temperature-pressure-compositionconditions. The nucleation and growth process would take place on a phantom crystalsurface after a zone melting recrystallization process and necessarily followed by shapeorientation relationship optimization (rather than crystallographic orientationrelationships) of the cliftonites by the host crystal, which could be accounted for by thehierarchical surface energies.