Benzerara, K; Menguy, N; Obst, M; Stolarski, J; Mazur, M; Tyliszczak, T; Brown Jr., GE; Meibom, A: Study of the crystallographic architecture of corals at the nanoscale by scanning transmission X-ray microscopy and transmission electron microscopy, Ultramicroscopy, 111(8), 1268-1275 (2011), online: 05.05.2011, doi:10.1016/j.ultramic.2011.03.023 [Link]

We have investigated the nanotexture and crystallographic orientation of aragonite in a coral skeleton using synchrotron-based scanning transmission X-ray microscopy (STXM) and transmission electron microscopy (TEM). Polarization-dependent STXM imaging at 40-nm spatial resolution was used to obtain an orientation map of the c-axis of aragonite on a focused ion beam milled ultrathin section of a Porites coral. This imaging showed that one of the basic units of coral skeletons, referred to as the center of calcification (COC), consists of a cluster of 100-nm aragonite globules crystallographically aligned over several micrometers with a fan-like distribution and with the properties of single crystals at the mesoscale. The remainder of the skeleton consists of aragonite single-crystal fibers in crystallographic continuity with the nanoglobules comprising the COC. Our observation provides information on the nm-scale processes that led to biomineral formation in this sample. Importantly, the present study illustrates how the methodology described here, which combines HRTEM and polarization-dependent synchrotron-based STXM imaging, offers an interesting new approach for investigating biomineralizing systems at the nm-scale.

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