Cronstedtite polytypes in the Paris meteorite

Abstract

The 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.

Deciphering the conditions of tochilinite and cronstedtite formation in CM chondrites from low temperature hydrothermal experiments

“…The SAED pattern along the [010] zone axis indicates the cell parameter c = 0.71 nm (Figs. 4e and 4f), consistent with typical terrestrial (Hybler et al 2000) and meteoritic cronstedtite (i.e., polytype 1T; Pignatelli et al 2018).…”

“…However, pure cronstedtite (i.e., cronstedtite with crystallo‐chemical characteristics similar to those reported for terrestrial ones) has recently been identified and characterized in CM Paris (Pignatelli et al. , ). The chemical composition of our synthetic cronstedtite is in good agreement with both terrestrial and pure cronstedtite in CM Paris (Hybler et al.…”

“…White diamonds represent the composition of meteoritic cronstedtite from the Paris CM chondrite (Pignatelli et al. ). Black circles represent the ideal chemical compositions of berthierine (“Be”; Brindley ), cronstedtite (“Cr”; Hybler et al.…”

Testing the genetic relationship between fluid alteration and brecciation in CM chondrites

“…; Pignatelli et al. , , ; Van Kooten et al. ), and oxygen isotopes are a powerful tool for constraining the physicochemical conditions (T, W / R , pH, etc.)…”

“…Aqueous alteration has been extensively studied in CM chondrites (e.g., McSween 1979a;Benedix et al 2003;Rubin et al 2007;Lee et al 2014;Pignatelli et al 2016Pignatelli et al , 2017Pignatelli et al , 2018Van Kooten et al 2018), and oxygen isotopes are a powerful tool for constraining the physicochemical conditions (T, W/R, pH, etc.) and relative timing of secondary phase precipitation.…”