Micro-Raman spectroscopy of pigments contained in different calcium carbonate polymorphs from freshwater cultured pearls

The metastable calcium carbonate polymorph vaterite has recently been found to occur commonly in freshwater cultured pearls from Japan and China. Organic pigment molecules in these vaterite regions of freshwater cultured pearls were analysed by resonance and near-resonance micro-Raman spectroscopy, in single spectra and in mapping modes and are compared with their aragonitic counterparts. Four different excitation wavelengths (487.9, 514.5, 532.2 and 632.8 nm) were used, resulting in differential increase of resolution for the pigments. Although vaterite areas were always lightly coloured (light yellow, light brown or white), ten different pigments were identified and a single colour is for…

Imitationen, Synthesen und Syntheseverfahren

Seit der Mensch die verschiedensten Materialien gebraucht, um Werkzeuge herzustellen, Gebaude zu erstellen, sich zu schmucken, werden Steine verwendet. Schon seit der Steinzeit werden Minerale zu Schmuck verarbeitet.

Structural characterization and chemical composition of aragonite and vaterite in freshwater cultured pearls

AbstractVaterite and aragonite polymorphs in freshwater cultured pearls from mussels of the genus Hyriopsis (Unionidae) were structurally and compositionally characterized by Raman spectroscopy, Micro computer tomography, high resolution field emission scanning electron microscopy, electron microprobe analysis and laser ablation inductively coupled plasma mass spectrometry. The appearance of vaterite in pearls is related to the initial stages of biomineralization, although we demonstrate that vaterite can not be a precursor to aragonite. It is not related to a particular crystal habit and therefore does not have a structural functionality in the pearls. Larger contents of elements typically…

Probing the Multiple Structures of Vaterite through Combined Computational and Experimental Raman Spectroscopy.

First-principles Raman spectra have been computed for several new vaterite structural models that have been recently proposed, and compared with spectra recorded on a set of biogenic, geological and synthetic samples. This set includes new measurements collected on Herdamania momus spicules (Great Barrier Reef, Queensland, Australia), which are known to have purity and crystallinity that are higher than for other biogenic samples. Overall, due to the close structural connection between the various models, the computed Raman spectra are found to be broadly similar. However, the spectra obtained for the two most stable models (monoclinic C2 and trigonal P3221, corresponding to two different p…

Amorphous calcium carbonate in the shells of adult Unionoida

Shells of adult individuals from two different bivalve families, Hyriopsis cumingii and Diplodon chilensis patagonicus, were studied by Micro-Raman spectroscopy and Focussed Ion Beam-assisted TEM. The shells contain amorphous calcium carbonate in a zone at the interface between the periostracum and the prismatic layer. In this area, the initial prism structures protrude from the inner periostracum layer and it is demonstrated that these structures systematically consist of highly disordered and amorphous calcium carbonate. Within this zone, ordered and disordered areas are intermingled discounting the existence of a crystallization front and favouring models of domainal crystallization proc…

Raman spectroscopy of synthetic, geological and biological vaterite: a Raman spectroscopic study

Raman spectroscopy was used to study vaterite samples of biological, geological and synthetic origin. The Raman band positions and the full width at half-maximum (FWHM) of the lattice modes and the internal modes of the carbonate ion of all specimens show no significant differences between vaterites of different origin. With increasing Mg concentrations, synthetic vaterite samples show increasing FWHM in the region of the lattice modes and the three ν1 bands, whereas no change in luminescence was detected. In contrast, in situ measurements of vaterite areas in freshwater cultured pearls (FWCPs) by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) together with the Rama…

Farbe und Lichteffekte

Abgesehen vom Diamanten, an dem vollige Farblosigkeit am meisten geschatzt wird, stellt die Farbe der Edelsteine den wichtigsten Schonheitsfaktor dar. Das begehrte Taubenblutrot eines wertvollen Rubins, das Kornblumenblau eines Saphirs, Smaragdgrun oder das zarte Blau eines Aquamarins haben trotz der Unterschiedlichkeit der Farbe eines gemeinsam: Es werden bestimmte Anteile aus dem weisen Licht geschwacht und/oder verstarkt, dabei entsteht farbiges Licht.

Nanostructure, composition and mechanisms of bivalve shell growth

Abstract Freshwater and marine cultured pearls form via identical processes to the shells of bivalves and can therefore serve as models for the biomineralization of bivalve shells in general. Their nanostructure consists of membrane-coated granules (vesicles) which contain amorphous calcium carbonate (ACC) at the beginning of the biomineralization sequence, preceding the crystallization of aragonite and vaterite. In contrast to the commonly accepted view, crystallization of ACC occurs rapidly and within the granular nano-compartments mediated by organic molecules much earlier than platelet formation. The interlamellar organic sheets in nacre that form the platelet structure of nacre themsel…

A Look Inside a Remarkably Large Beaded South Sea Cultured Pearl

Amorphous, nanocrystalline and crystalline calcium carbonates in biological materials

Raman spectroscopy is a powerful tool in identifying different calcium carbonate polymorphs. Here, the method is applied to cultured pearls from freshwater (genus Hyriopsis) and marine bivalve species (Pinctada maxima) as well as to shells of Diplodon chilensis patagonicus bivalves. Raman spectra for vaterite, detected for the first time in an adult shell, and amorphous calcium carbonate (ACC) are discussed. Results for ACC are compared with those of synthetically produced ACC and with the Raman spectroscopic features of stable biogenic ACC from the crustacean Porcellio scaber. Decomposition of the most intense signal of all calcium carbonate polymorphs—the ν1 symmetric stretching mode of t…

Die optischen Eigenschaften der Edelsteine

Die wichtigsten Eigenschaften der Edelsteine wie z. B. Farbe, Glanz, Brillanz, Lichtbrechung und Dispersion („Feuer“) sind optische Eigenschaften und beruhen auf den Wechselwirkungen zwischen Licht und Edelstein bzw. allgemein Materie. Will man diese Besonderheiten richtig erfassen, so sind zunachst einige physikalische Grundbegriffe naher zu betrachten und die Frage nach dem „Wesen“ des Lichts und seines Verhaltens beim Durchgang durch die Kristalle zu beantworten.