Fig. 7.

SEM images of the native surface of T. peltata (Tp) skeleton showing the dual mechanism of particle attachment and ion-by-ion filling in forming coral skeleton fibers. The outer surface of each fiber in A and B appears as a euhedral pseudohexagonal prism, with a smooth lateral surface that is space-filling; thus, it must have grown by both particle attachment and ion-by-ion filling. Interspersed with euhedral crystals are nonspace-filling nanoparticles. Increasing magnification images in A1–A4 and B1–B4 show where on the native surface the images in A and B were acquired. Particles may attach preferentially in euhedral pseudohexagonal prism geometry, thus, surfaces parallel to the outer pseudohexagonal edges are recognizable, as indicated by arrows in A. A false-color version of B is presented as SI Appendix, Fig. S3 to indicate space-filling and nonspace-filling crystals, both of which have at least one nanoparticulate side.