Recent detections of plagioclase on various planetary bodies by infrared spectroscopy (e.g. Payré et al. (2024), Minerals) call for a better understanding of the mineral's spectral signature. Since the study of terrestrial analog samples proved to be limited by alteration and signal mixing (e.g., Barthez et al. (2023), JGR: Planets), we focus on synthesizing a range of plagioclase feldspars to investigate the effects of their composition (An#, iron content and speciation) on their spectral properties. This aims to produce equilibrated crystals spatially resolved by the laboratory spectral cameras (https://crpg.univ-lorraine.fr/en/hyperspectral-remote-sensing-en/), thus larger than 32µm.

Reagent grade oxides were mixed and homogenized in a muffle furnace for both plagioclase endmembers compositions, anorthite and albite, with different iron-enrichments. Small pellets of the resulting starting glass materials were then hung with platinum wire loops on a ceramic rod to conduct dynamic crystallization experiments in a 1-atm vertical furnace. These runs were performed under two different redox conditions: 1) in atmospheric air, ensuring oxidizing conditions versus 2) in CO-CO2 gas mixtures, regulating reduced conditions (between FMQ and FMQ-2). Quenched samples were glued onto glass plates for polishing, characterization (optical microscope, SEM), and spectral analyses.

Results show that millimetric euhedral anorthites can be synthesized, regardless of the iron levels or redox states that were set, with initial superheating and slow cooling rates (1°C/h to 15°C/h). This allows for the study of iron partitioning between calcic plagioclase - melt and between crystallographic sites. The crystal size is also sufficient to investigate the mineral's spectral properties, although their transparency posed new challenges. The sodic composition, however, did not form large and idiomorphic albites despite the various heating protocols tested: textures range from dendritic to spherulitic with 25µm equilibrated cores. The viscosity of this anhydrous albitic melt seems to prevent the diffusion of elements and thus crystal growth.