Elemental composition of manganese- and phosphorus-rich nodules in the Knockfarril Hill member, Gale crater, Mars

The Mars Science Laboratory rover Curiosity encountered nodules rich in manganese and phosphorus while exploring the Knockfarril Hill member of Gale crater on Mars. Deconvolution of X-ray spectroscopy data acquired by the Alpha Particle X-ray Spectrometer (APXS) at the spectral level indicate P2O5 concentrations possibly in excess of 18 wt% and MnO exceeding 8 wt%. The nodules occur intermittently in-mm-thick layers concordant with the sedimentary laminae, extending up to-10 cm laterally. Calcium sulfate associated with the nodules is interpreted as having precipitated from fluid that infiltrated between the nodule-bearing bedding planes in a separate and subsequent fluid event. Though the Mn-and P-bearing phase(s) was(were) not definitively iden-tified by X-ray diffraction, evolved gas analyses show that the oxidation state of Mn is most likely 2+.