The crystallographic orientations of calcite in several major groups of Cretaceous heterococcoliths in chalk from Dover, England, were investigated using electron backscatter diffraction (EBSD) and field-emission scanning electron microscope (FE-SEM) stereo-photogrammetry. The previous crystallographic classification of coccoliths according to sub-vertical and sub-radial orientations of the c-axis (V-units and R-units, respectively) were further divided into several types according to the orientations and inclination angles of c- and ai-axes. As a common property, all units were likely aligned with the calcite <4 8 1̅> direction along coccolith rings. Most units of heterococcoliths developed calcite rhombohedral surface {1 0 1̅ 4} planes, while V-units of imbricating muroliths and R-units of a placolith developed calcite {2 1̅ 1̅ 0} planes. The results indicate the crystallographic variability corresponding with the morphological variations during the 230 million years of heterococcolith history; however, the morphologies and crystallographic properties are constrained by the alignment of the calcite <4 8 1̅> direction along the coccolith ring.

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