The formation of impact coesite

Abstract Coesite in impact rocks is traditionally considered a retrograde product formed during pressure release by the crystallisation of an amorphous phase (either silica melt or diaplectic glass). Recently, the detailed microscopic and crystallographic study of impact ejecta from Kamil crater and...

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Autores principales:	F. Campanale, E. Mugnaioli, M. Gemmi, L. Folco
Formato:	article
Lenguaje:	EN
Publicado:	Nature Portfolio 2021
Materias:	Medicine R Science Q
Acceso en línea:	https://doaj.org/article/cdf0e856fae14f29bc69ebf991c0722a
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spelling	oai:doaj.org-article:cdf0e856fae14f29bc69ebf991c0722a2021-12-02T17:06:25ZThe formation of impact coesite10.1038/s41598-021-95432-62045-2322https://doaj.org/article/cdf0e856fae14f29bc69ebf991c0722a2021-08-01T00:00:00Zhttps://doi.org/10.1038/s41598-021-95432-6https://doaj.org/toc/2045-2322Abstract Coesite in impact rocks is traditionally considered a retrograde product formed during pressure release by the crystallisation of an amorphous phase (either silica melt or diaplectic glass). Recently, the detailed microscopic and crystallographic study of impact ejecta from Kamil crater and the Australasian tektite strewn field pointed in turn to a different coesite formation pathway, through subsolidus quartz-to-coesite transformation. We report here further evidence documenting the formation of coesite directly from quartz. In Kamil ejecta we found sub-micrometric single-coesite-crystals that represent the first crystallization seeds of coesite. Coesite in Australasian samples show instead well-developed subeuhedral crystals, growing at the expenses of hosting quartz and postdating PDF deformation. Coesite (010) plane is most often parallel to quartz {10–11} plane family, supporting the formation of coesite through a topotactic transformation. Such reaction is facilitated by the presence of pre-existing and shock-induced discontinuities in the target. Shock wave reverberations can provide pressure and time conditions for coesite nucleation and growth. Because discontinuities occur in both porous and non-porous rocks and the coesite formation mechanism appears similar for small and large impacts, we infer that the proposed subsolidus transformation model is valid for all types of quartz-bearing target rocks.F. CampanaleE. MugnaioliM. GemmiL. FolcoNature PortfolioarticleMedicineRScienceQENScientific Reports, Vol 11, Iss 1, Pp 1-8 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Medicine R Science Q
spellingShingle	Medicine R Science Q F. Campanale E. Mugnaioli M. Gemmi L. Folco The formation of impact coesite
description	Abstract Coesite in impact rocks is traditionally considered a retrograde product formed during pressure release by the crystallisation of an amorphous phase (either silica melt or diaplectic glass). Recently, the detailed microscopic and crystallographic study of impact ejecta from Kamil crater and the Australasian tektite strewn field pointed in turn to a different coesite formation pathway, through subsolidus quartz-to-coesite transformation. We report here further evidence documenting the formation of coesite directly from quartz. In Kamil ejecta we found sub-micrometric single-coesite-crystals that represent the first crystallization seeds of coesite. Coesite in Australasian samples show instead well-developed subeuhedral crystals, growing at the expenses of hosting quartz and postdating PDF deformation. Coesite (010) plane is most often parallel to quartz {10–11} plane family, supporting the formation of coesite through a topotactic transformation. Such reaction is facilitated by the presence of pre-existing and shock-induced discontinuities in the target. Shock wave reverberations can provide pressure and time conditions for coesite nucleation and growth. Because discontinuities occur in both porous and non-porous rocks and the coesite formation mechanism appears similar for small and large impacts, we infer that the proposed subsolidus transformation model is valid for all types of quartz-bearing target rocks.
format	article
author	F. Campanale E. Mugnaioli M. Gemmi L. Folco
author_facet	F. Campanale E. Mugnaioli M. Gemmi L. Folco
author_sort	F. Campanale
title	The formation of impact coesite
title_short	The formation of impact coesite
title_full	The formation of impact coesite
title_fullStr	The formation of impact coesite
title_full_unstemmed	The formation of impact coesite
title_sort	formation of impact coesite
publisher	Nature Portfolio
publishDate	2021
url	https://doaj.org/article/cdf0e856fae14f29bc69ebf991c0722a
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The formation of impact coesite

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