Terrestrial weathering of Antarctic stone meteorites: Formation of Mg-carbonates on ordinary chondrites

White efflorescences of weathering origin occur superposed on fusion crusts, or along fractures in the interiors, of approximately 5% of all meteorites in the US Antarctic collection. Efflorescences from equilibrated ordinary chondrites consist of the hydrous Mg-carbonates nesquehonite (±hydromagnesite). X-ray diffraction and scanning electron microscope studies of efflorescences from LEW 85320 (H5) show abundant elongate prismatic crystals of nesquehonite (idiomorphic, not pseudomorphous after lansfordite), with minor local encrustations of hydromagnesite.