Texture Analysis of Polycrystalline Vaterite Spherulites from Lake Sturgeon Otoliths

Abstract

Fish otoliths, or ear bones, are comprised of the CaCO 3 polymorphs (aragonite, calcite and vaterite), which can occur either alone or in combination. The polymorph phase abundance in an otolith depends on, as yet, unexplained genetic and environmental factors. Most fish otoliths are comprised of the densest CaCO 3 polymorph, aragonite. Sturgeon otoliths, on the other hand, contain significant amounts of the rare and the structurally enigmatic polymorph, vaterite. Sturgeon otoliths are frequently comprised of agglomerations of small microcrystalline vaterite spherulites (<300 μ m in diameter), that range in shape from nearly perfect spheres to oblate spheroids. These spherulites are similar to the synthetic vaterite microspheres employed in laser trapping applications. Vaterite spherulites from both hatchery-reared (juvenile) and wild (adult) Lake Sturgeon exhibit extreme crystallographic texture as evidenced by X-ray diffraction patterns and their reconstructed pole-figures determined here. The vaterite crystallites making up the spherulites have excellent registry in both the axial and equatorial directions. Whether synthesized or natural, the texture manifested in these spherulites suggests that vaterite nucleates and grows similarly in vivo otolith formation as well as from laboratory synthesis. The uniaxial optical character of the vaterite spherulites, confirmed by these diffraction experiments and combined with their large birefringence, makes them well suited for laser trapping applications.

Assembly of the Intraskeletal Coral Organic Matrix during Calcium Carbonate Formation

“…This suggests that the spherulitic crystals, imaged by SEM, consist of crystallites that may nucleate and grow at the substrate surface, which induces their preferential orientation (Figure S3). This preferential orientation was recently observed in vivo at Lake Sturgeon otolith formation and in synthetic crystals, where vaterite spherulites formed by crystallites . This contrasts with the more common spherulitic growths associated with radiating or concentric textures .…”

“…This preferential orientation was recently observed in vivo at Lake Sturgeon otolith formation and in synthetic crystals, where vaterite spherulites formed by crystallites. 46 This contrasts with the more common spherulitic growths associated with radiating or concentric textures. 47 On the other hand, the distribution of the spotty diffraction signals of calcite indicates that it forms crystallites having the (104) face mainly parallel to the silicon surface, together with a small fraction of small crystallites almost randomly oriented, which produce weaker almost uniform (ring) signals.…”

Two-Level Optical Birefringence Created by Evaporation-Induced Polymer Crystallization in Sessile Droplets

“…The circular symmetry in spherulites results in the well-known Maltese cross and centrosymmetric birefringence under a cross-polarized optical microscope. Great efforts have been made to elucidate the relationship between the lamellar orientation and the spherulitic birefringence in polymer melts, blends, and solution-casting films. − Those fundamental studies are the basis to understand the optoelectronic or electrooptical properties in semiconductors, solar cells, and light-emitting devices. − Recent progress in droplet-processing techniques, i.e., inkjet printing, , 3D printing, , ultrasonic spray, and microfluidics, , further requires precise control of polymer crystals and optical properties on micro- or nanometer scales, which is an emerging area to be explored.…”

Characterization of golden vaterite by the extended Maxwell Garnett formalism

“…Vaterite is a naturally occurring polymorph of calcium carbonate which can be found in certain biological tissues [1][2][3]. Vaterite monocrystals can self-assemble to form polycrystalline spherulites which are highly porous [4].…”