Bizarre artefacts in transmission electron microscopy preparation and observation of geological samples

Several artefacts occurring during TEM sample preparation by ion-milling and observation, which cannot be straightforwardly discerned from genuine properties of the sample, are presented and discussed, with the aim to warn unexperienced microscopists against misinterpretation of TEM data. The cases presented here span from typical material sputtering and redeposition during ion-milling sample preparation, or sample decomposition under the electron beam, to more exotic cases of sample recrystallization during observation or during storage within the grid box. Overall, 15 different case studies, categorized among artefacts produced during (i) preparation, (ii) observation, (iii) microanalysis and (iv) sample storage are illustrated and discussed. The paper ends with recommendations on how minimize both preparation- and observation-induced artefacts, with specific mention to minerals.