IDENTIFYING PARTIALLY CHLORITIZED SMECTITE ON THE MARTIAN SURFACE

Clay minerals have been detected on Mars via orbital surveys and rover missions (e.g., Ehlmann et al. 2013; Vaniman et al., 2014). Since these clays are hydrous alteration products of Mars’ basaltic crust, their presence gives insight into the planet’s aqueous history. Characterizing the clay mineral structures and chemical composition can provide specific details about formation mechanisms and diagenetic processes.

The most common clay minerals on Mars are smectites and chlorites (Ehlmann et al., 2013). Smectite is a swelling clay, whereas chlorite has a brucite- or gibbsite-like interlayer structure that does not expand. There is also evidence for smectite/chlorite integrades (e.g., Bristow et al., 2015), which may include smectites that have octahedral pillars within some interlayer sites. Investigating these intergrades in the laboratory is essential for identifying them on the Martian surface with orbital and landed data and for distinguishing partially chloritized smectite from discrete smectite and chlorite.

Using three types of terrestrial smectites, we created partially chloritized smectites by adding Mg²⁺ and OH^- to a clay suspension to produce MgOH₂ pillars. We pillared the smectites to various degrees by altering the Mg²⁺/OH^- ratio. We chose Mg²⁺ as the cation because mafic minerals are abundant in Mars’ crust and Curiosity discovered evidence for early diagenesis in Mg-bearing fluids in Gale crater (e.g., Leveille et al., 2014). We then compared X-ray diffraction, evolved gas analysis, and visible-near infrared data to data returned from Mars in order to identify and characterize the relative chloritization of the Martian clay mineral intergrades.