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. Yet, 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 state-of-the-art electron tomography, we examined
multiple stages of coccolith development in 3D. We found that the crystals
are expressing 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 show that manipulations
of growth kinetics can yield complex crystalline morphologies.