Progressive aqueous alteration and iron oxidation record in the matrix of Mukundpura CM2 chondrite, a new fall

Abstract

• Mukundpura- a matrix-rich CM2, fresh fall. • Matrix shows evidences of progressive alteration. • Iron speciation record is consistent with presence of Cronstedtite. The matrices of CM chondrites are fine-grained and have undergone aqueous alteration. Based on mineral chemical composition of matrix phyllosilicate of Mukundpura CM2, the evidence of progressive aqueous alteration is understood and also reflected in gradual changes in S/SiO 2 and FeO/SiO 2 ratios. Further, we performed X-ray absorption near-edge spectroscopy at the Fe K-edge to explain the redox state of the phyllosilicate. The Iron Oxidation Index of Mukundpura yields 2.423 and the Fe +3 / Fe +2 ratio is 0.733. The Fe speciation in phyllosilicate is also sensitive to the degree of aqueous activity. Our data are consistent with the presence of Cronstedtite and Tochilinite-Cronstedtite intergrowths in the matrix suggested for different extent of alteration and recorded history of pervasive aqueous alteration in the asteroidal parent body.