Original paper
Cronstedtite polytypes in the Paris meteorite
Pignatelli, Isabella; Mugnaioli, Enrico; Marrocchi, Yves
European Journal of Mineralogy Volume 30 Number 2 (2018), p. 349 - 354
46 references
published: Aug 20, 2018
published online: May 4, 2018
manuscript accepted: Oct 24, 2017
manuscript revision received: Oct 24, 2017
manuscript received: Sep 16, 2017
Abstract
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 2M 1 polytypes be recognised. TEM-EDX data indicate that the chemical composition of the crystals is similar, regardless of their polytypic sequence.
Keywords
cronstedtite • MDO polytypes • 3D electron diffraction • Paris meteorite