Learning crystallography from sea urchin

The skeleton of sea urchin spines is composed of large single crystals of Mg-rich calcite, which have smooth, continuously curved surfaces and form a three-dimensional fenestrated mineral network. Spines of the echinoids//. trigonariusmAH. mammillatus 

A unique transformation from disordered amorphous structure to ordered crystalline structure occurs. These amorphous to crystalline phase transformation from the liquid state can teach us to produce highly ordered and well-oriented synthetic nanomaterials and composites. 

In order to simulate the amorphous to crystalline transformation, Milev et al. developed a novel method to produce single-phase, nano-sized, plate-like, mixed A-B-type carbonate-containing apatite (CAp) similar to bone apatite by using sol-gel technology (Milev et al., 2003). The methodology emulates biomineralization, where topotactic transition from amorphous to octacalcium phosphate (OCP) than to hydroxyapatite (HAp), which is believed to occur in vivo. 

Raz et al. (2003) reported the transient phase of amorphous calcium carbonate in sea urchin larval spicules and the involvement of proteins and magnesium ions in its formation and stabilization. 

This was further confirmed by a study of Gong et al. (2012) using X-ray absorption near-edge structure (XANES) spectroscopy and photoelectron emission microscopy 

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