Synthesis of opal under geologically relevant conditions for the fossilization of organic molecules and reconstruction of past climates on Mars and Earth

Alteration minerals potentially record past climate conditions in geological sequences. This ability allows to identify pas climate on early Earth and also other planetary bodies such as Mars. Among these alteration minerals, opal remain uneasy to use as a climate proxy especially because it has not been yet synthetized in the laboratory under conditions that rigorously fit the natural, geological conditions. Recent works at our laboratory (including those of Dr. Simon Gouzy) provided significant advances by opening the way of synthesis under ambient temperature, in water, and starting with materials as close to naturals as possible. Also, these pioneer works also attempted to incorporate organic molecules in these synthetic opals, which opens the way for the study of the hability of ancient opal to fossilize organic molecules. 

The objectives of this project are first to identify in detail the genesis conditions of opal in order to use the geochemical and spectroscopic properties of natural samples as proxies of their conditions of formation. In particular we will determine the ranges of temperature, pH and Eh in which these properties are obtained by synthesis in the laboratory. We will then characterize in what manner organic molecules are incorporated in opal (inside silica grains, in the silica gel, or isolated patches dispersed in opal), as this may strongly influence the potential for OM preservation along time. 

To reach these objectives, we will need to:

• Be able to incorporate chemical impurities (Al, Ca…) in synthetic opal
• Be able to synthetize opal-CT, cryptocrystalline variety of opal never obtained by synthesis
• Be able to incorporate various organic molecules and characterize their typology.

This work will require the use of techniques for synthesis in aqueous medium, and techniques of materials characterization: optical and electronic microscopies (SEM, TEM), optical and vibrational spectroscopies (FTIR, Raman), combined microscope and spectroscopy (AFM-IR), and elemental analysis (ICP-OES, ICP-MS, EDX).

Education in Geosciences including a solid background in mineralogy (with characterization techniques), surface-related alteration processes, geochemistry (trace elements and isotopic). Knowledge in organic chemistry may be appreciated.