In various mineralizing marine organisms, calcite or aragonite crystals form through the initial deposition of amorphous calcium carbonate (ACC) phases with different hydration levels. Using X-ray PhotoEmission Electron spectroMicroscopy (X-PEEM), ACCs with varied spectroscopic signatures were previously identified. In particular, ACC type I and II were recognized in embryonic sea urchin spicules. ACC type I was assigned to hydrated ACC based on spectral similarity with synthetic hydrated ACC. However, the identity of ACC type II has never been unequivocally determined experimentally. In the present study we show that synthetic anhydrous ACC and ACC type II identified here in sea urchin spines, have similar Ca L _2,3-edge spectra. Moreover, using X-PEEM chemical mapping, we revealed the presence of ACC-H₂O and anhydrous ACC in growing stereom and septa regions of sea urchin spines, supporting their role as precursor phases in both structures. However, the distribution and the abundance of the two ACC phases differ substantially between the two growing structures, suggesting a variation in the crystal growth mechanism; in particular, ACC dehydration, in the two-step reaction ACC-H₂O → ACC → calcite, presents different kinetics, which are proposed to be controlled biologically.

Magnetic skyrmions are topologically protected spin textures that exhibit fascinating physical behaviours and large potential in highly energy-efficient spintronic device applications. The main obstacles so far are that skyrmions have been observed in only a few exotic materials and at low temperatures, and fast current-driven motion of individual skyrmions has not yet been achieved. Here, we report the observation of stable magnetic skyrmions at room temperature in ultrathin transition metal ferromagnets with magnetic transmission soft X-ray microscopy. We demonstrate the ability to generate stable skyrmion lattices and drive trains of individual skyrmions by short current pulses along a magnetic racetrack at speeds exceeding 100 m s(-1) as required for applications. Our findings provide experimental evidence of recent predictions and open the door to room-temperature skyrmion spintronics in robust thin-film heterostructures.