Classification of hydrous meteorites (CR, CM and C2 ungrouped) by phyllosilicate fraction: PSD-XRD modal mineralogy and planetesimal environments

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K.T. Howard, C.M.O’D. Alexander, D.L. Schrader, K.A. Dyl
DOI: 10.1016/j.gca.2014.10.025
available online 4 November 2014

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Here we report the bulk mineralogies and degrees of hydration in 37 different carbonaceous chondrites: Renazzo-like (CR), Mighei-like (CM), and ungrouped (type 2) samples. This is achieved by quantifying the modal abundances of all major (phases present in abundances >1wt.%) minerals using Position Sensitive Detector X-ray Diffraction (PSD-XRD). From these modal abundances, a classification scheme is constructed that is based on the normalized fraction of phyllosilicate (View the MathML sourcetotalphyllosilicate/totalanhydroussilicate+totalphyllosilicate). Samples are linearly ranked from type 3.0 – corresponding to a phyllosilicate fraction of <0.05, to type 1.0 - corresponding to a total phyllosilicate fraction of >0.95. Powdered meteorite samples from any hydrated carbonaceous chondrite group can be ranked on this single classification scale. The resulting classifications for CRs exhibit a range from type 2.8 to 1.3, while for CMs the range is 1.7–1.2.

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