Origin of the red colour in a red limestone from the Vispi Quarry section (central Italy): A high-resolution transmission electron microscopy analysis

► We use HRTEM to study the colourizing mechanism of CORBs. ► We identified two types of the hematite origin: continental origin and autogenous origin. ► The distribution of continental origin hematite is extremely heterogeneous in red limestone. ► We find that the nano- grains of hematite endowed the limestone with homogeneous red colour.