How does crystallinity propagate through the amorphous sea urchin larval spicule?

Amorphous precursors explain unusual morphology of biominerals

amorphous precursors have now been observed in tooth enamel, in zebra fish fin bones, in mollusk shells, in the chiton teeth, shark otoliths, sea urchin spines, sea

urchin spicules, etc.

sea urchin larval spicules (above) diffract like single crystals of calcite, and they are 99.9w% calcite, yet their morphology is very different from calcite rhombohedra.

Crystallinity propagates through ACC via secondary nucleation

PEEM-3 data48-hr spicules, 20-nm pixels

the crystalline pattern follows a random walkno isolated crystal units

fractal network percolation

each pixel was assigned to either anhydrous ACC or calcite, using singular value decomposition (SVD)

Yael Politi, Rebecca A. Metzler, Mike Abrecht, Benjamin Gilbert, Fred Wilt, Irit Sagi, Lia Addadi, Steve Weiner, and P.U.P.A. Gilbert. Mechanism of transformation of amorphous calcium carbonate into calcite in the sea urchin larval spicule. Procs. Natl. Acad. Sci. USA 105, 17362-17366, 2008.