Cronstedtite polytypes in the Paris Meteorite

We present the first detailed crystallo-chemical and crystallographic description of cronstedtite with extraterrestrial origin. The analysed crystals occur as pseudomorphs after anhydrous silicates in the Paris meteorite, which is the least altered carbonaceous chondrite currently known. Three-dimensional electron diffraction data have been collected by electron diffraction tomography and used to identify the cronstedtite polytypes, because of their small size. All identified polytypes are MDO (Maximum degree of order), and the most abundant one is 1T. Many other crystals also belong to the Bailey's group (or OD subfamily) C, but their stacking disorder hampers the polytype identification. Only in one crystal could the 3T and 2M1 polytypes be recognised. TEM-EDX data indicate that the chemical composition of the crystals is similar, regardless of their polytypic sequence.