title: Transformation mechanism of amorphous calcium carbonate into calcite in the sea urchin larval spicule.
abstract: Sea urchin larval spicules transform amorphous calcium carbonate (ACC) into calcite single crystals. The mechanism of transformation is enigmatic: the transforming spicule displays both amorphous and crystalline properties, with no defined crystallization front. Here, we use X-ray photoelectron emission spectromicroscopy with probing size of 40-200 nm. We resolve 3 distinct mineral phases: An initial short-lived, presumably hydrated ACC phase, followed by an intermediate transient form of ACC, and finally the biogenic crystalline calcite phase. The amorphous and crystalline phases are juxtaposed, often appearing in adjacent sites at a scale of tens of nanometers. We propose that the amorphous-crystal transformation propagates in a tortuous path through preexisting 40- to 100-nm amorphous units, via a secondary nucleation mechanism.
authors.affiliation: Department of Structural Biology, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Yael
authors.initials: Y
authors.lastname: Politi
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Metzler
authors.forename: Mike
authors.initials: M
authors.lastname: Abrecht
authors.forename: Benjamin
authors.initials: B
authors.lastname: Gilbert
authors.forename: Fred H
authors.initials: FH
authors.lastname: Wilt
authors.forename: Irit
authors.initials: I
authors.lastname: Sagi
authors.forename: Lia
authors.initials: L
authors.lastname: Addadi
authors.forename: Steve
authors.initials: S
authors.lastname: Weiner
authors.forename: P U P A
authors.initials: PU
authors.lastname: Gilbert
authors.forename: Pupa
authors.initials: P
authors.lastname: Gilbert
mesh_terms: D000825:Animal Structures / Q000737:chemistry / Q000648:ultrastructure*; D000818:Animals; D002113:Calcification, Physiologic; D002119:Calcium Carbonate / Q000737:chemistry*; D004577:Electron Probe Microanalysis; D007814:Larva / Q000737:chemistry / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D047270:Strongylocentrotus purpuratus / Q000737:chemistry*
chemical_list: D002119:Calcium Carbonate