Talc has been known to nucleate poly(ethylene terephthalate) (PET) for a long time, but the exact nucleation mechanism involved had remained unknown. This study presents evidence of an epitaxial relationship between the polymer and the inorganic substrate. Electron diffraction results suggest a contact between the (100) PET plane and (001) talc basal plane as well as an alignment of the [001] PET chain axis with the three quasi-hexagonal directions of talc. Transmission electron microscopy confirms these findings but highlights some matching imperfections, partly due to irregularities of the talc lattice. Besides, it suggests a tilt of the polymer chain axis with respect to the lamellar fold surface. The long period of PET lamellar stacks is also noticeably larger on the talc contact plane.