Imaging reveals how coral crystals grow

Understanding crystals’ formation is important to the pharmaceutical and food industries, but it also elucidates the resilience of animals that make hard skeletons, including corals. This week at the American Chemical Society Fall 2021 meeting, Pupa Gilbert, a physicist at the University of Wisconsin–Madison, described her work using corals as a model system to study crystal growth.

Speaking in a Division of Geochemistry session, Gilbert showed a striking, tie-dye-like rainbow image detailing the orientation of crystals of aragonite, a form of calcium carbonate, in a coral skeleton. Each patch of color in the image, made using the synchrotron at Lawrence Berkeley National Laboratory, is a crystallite made up of a group of uniformly oriented, needle-shaped aragonite crystals. The crystallites radiate outward from central points or from flat or curved surfaces. When the needles begin growing, Gilbert found, all orientations are possible. But radially arranged aragonite needles have more space to grow—other needles run into each other and stay small. As crystallization continues, big crystals get bigger, eating up the small ones (Acta Biomater. 2021, DOI: 10.1016/j.actbio.2020.06.027).

This arrangement of needle-shaped crystals, called a spherulite, is also formed in chocolate and in drugs including testosterone and aspirin. Basic research into spherulite formation could give insights into corals’ resilience in the face of climate change. “We’re interested in how corals form their skeletons and how they can adapt to ocean acidification,” Gilbert said.