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A diffusionless transformation in normal alkane: we observed an interesting pattern of twinned domains that occurs in the phase sequence of a particular n-alkane, tricosane (C₂₃H₄₈). Phase transitions between this twinned regime and one of its neighboring phases preserve atomic-scale features such as growth steps, indicating that the regime is entered via a diffusionless (martensitic-like) transition. This is an optical microscopy image, which shows a pattern of stripes with a spacing of ˜1 µm organized into domains with sizes of tens of micrometers, as shown in figure at a temperature ˜42°C, stripes are separated into domains separated by two types of twin boundaries.