MS15-P07 Investigating the primitive Earth through crystals Fermin Otalora (Laboratorio de Estudios Cristalográficos. Instituto Andaluz de Ciencias de la Tierra. CSIC/UGr, Armilla, Granada, Spain) Juan Manuel García Ruiz (Laboratorio de Estudios Cristalográficos. Instituto Andaluz de Ciencias de la Tierra. CSIC/UGr, Armilla, Granada, Spain)email: ferminotalora@gmail.com

Crystallography has a long history in providing knowledge and methods for applications in other disciplines. The identification of minerals using X-ray diffraction is one of the most important contributions of crystallography to Earth Sciences. But crystals deteriorate during during the long geological history, getting dissolved, replaced or deeply modified. After these process, diffraction information is restricted or Inexistent. This happen specially for crystals in very old samples, like the Archean rocks (3500 My) that we have investigated. In these cases, the real crystals disapeared long time ago and the morphology of the crystal casts provides the only crystallographic information on the original mineral phase and the environment of crystal growth. Here, we investigate crystal pseudomorphs and crystal casts found in a carbonate-chert facies from the 3.48 Ga old Dresser Formation (Pilbara Craton, Australia) that host some of the oldest remnants of life. Any information obtained from these casts on the atmosfere or the sea were crystals grew is telling us about the environment where life started. We have used a combination of X-ray microtomography, energy-dispersive X-ray spectroscopy, and crystallographic methods to reveal the original phases of these Archean pseudomorphs. We found with a high degree of confidence that the original crystals forming in Archean times were hollow aragonite.

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Keywords: Aragonite, crystal morphology, X-ray tomography