Cronstedtite polytypes in the Paris meteorite

International audienceThe first detailed crystallo-chemical and crystallographic description of cronstedtite with extraterrestrial origin has been presented in this study. The analysed crystals have been found in the Paris meteorite, which is the least altered carbonaceous chondrite currently known, and they result from the pseudomorphism of anhydrous silicates. 3D electron diffraction collected by combining electron diffraction tomography (EDT) and precession electron diffraction (PED) are used to identify the cronstedtite polytypes, because of their small size. All identified polytypes are MDO, and the most abundant one is 1T. Many other crystals also belong to the subfamily C, but their stacking disorder hampers the polytype identification. Only in a crystal, the 3T and 2M 1 polytypes are recognised. TEM-2 EDX data indicate that the chemical composition of the crystals is similar, regardless their polytypic sequence