The surface structure of a centimetre sized crystal of talc from the Trimouns deposit (Ariége, France) was imaged by atomic force microscopy. The direct image shows detailed characteristics of clay tetrahedral surfaces. The unit-cell dimensions obtained using atomic force microscopy (aor = 5.47± 0.28 and bor = 9.48 ± 0.28 Å) are found to be slightly higher, with a higher uncertainty, than those obtained using X-ray diffraction (aor = 5.288 ± 0.007 and bor = 9.159 ± 0.010 Å) and selected-area electron diffraction (aor = 5.32 ± 0.03 and bor = 9.22 ± 0.05 Å). Talc has a quasi-ideal surface, free from strong structural distortion, as compared to most other clay minerals, and is unlikely to have surface relaxation. The observation, on the obtained image, of apparent cell-dimension enlargement is then more likely attributed to instrumental artefacts, also responsible for scattered values of unit-cell parameters, rather than related to any surface structural features. The interpretation of apparent changes in unit-cell dimensions in terms of structural features for other clay minerals, in which such structural deformations is common (micas, kaolinites and chlorites), should therefore be done with extreme care.

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