Complex morphologies of biogenic crystals emerge from anisotropic growth of symmetry-related facets

Directing crystal growth into complex morphologies is challenging, as crystals tend to adopt thermodynamically stable morphologies. However, many organisms form crystals with intricate morphologies, as exemplified by coccoliths, microscopic calcite crystal arrays produced by unicellular algae. The complex morphologies of the coccolith crystals were hypothesized to materialize from numerous crystallographic facets, stabilized by fine-tuned interactions between organic molecules and the growing crystals. Using electron tomography, we examined multiple stages of coccolith development in three dimensions. We found that the crystals express only one set of symmetry-related crystallographic facets, which grow differentially to yield highly anisotropic shapes. Morphological chirality arises from positioning the crystals along specific edges of these same facets. Our findings suggest that growth rate manipulations are sufficient to yield complex crystalline morphologies.

Automated summary

This study reveals that complex crystalline morphologies can be achieved by manipulating the growth rate. Using electron tomography, the researchers examined the development of coccolith crystals in three dimensions and found that the crystals express only one set of symmetry-related crystallographic facets, with the positioning of the crystals along specific edges contributing to morphological chirality.