T. Soldatos

Role of polyenes in the coloration of cultured freshwater pearls

The exact nature of pigments present in cultured freshwater pearls is still not well known. We examined 21 untreated cultured freshwater pearls from Hyriopsis of typical colors by diffuse reflectance UV-Vis-NIR and Raman scattering measurements, at high resolution. The objective was to establish the relation between color and the nature of the pigment mixture in pearls, using strictly non-destructive methods. All natural color samples show the two major Raman resonance features of unmethylated (unsubstituted) polyenes, not carotenoids. Their general chemical formulae are R-(-CH=CH) N -R′ with N = 6 to 14 and they give absorptions from violet to yellow–green. Each color is due to a mixture of pigments, not a single pigment. Different colors are explained by different mixtures. Each pigment identified by Raman spectroscopy can be related to a specific absorption with apparent maximum in the range 405–568 nm, thus absorbing from violet to yellow–green. This is the first study of the precise relation between Raman and diffuse reflectance spectra of cultured freshwater pearls.

Geochemistry and evolution of the fanos granite, N. Greece

SummaryThe Fanos granite, a Jurassic pluton composed of high silica fine- to coarse-grained leucogranites, is associated with and intrudes the Mesozoic Guevgueli ophiolitic complex. Discriminant diagrams indicate a collision related plate tectonic environment for the rocks studied. They are peraluminous with calc-alkaline affinities. Major and trace element behaviour suggest a fractional crystallization process for the evolution of the Fanos granite. Petrographic calculations, based on major elements, require 32% crystal accumulation mainly of plagioclase, K-feldspar and biotite for a direct model, while for a two-step model 21% and 14% crystal cumulate is required for the first and the second step respectively.ZusammenfassungDer jurassische Fanos-Granit ist ein fein- bis grobkörniger Leukogranit mit hohem Silikatanteil. Er ist mit dem mesozoischen Ophiolithkomplex von Guevgueli, mit dem er in instrusivem Kontakt steht, verknüpft.Diskriminierungsdiagramme weisen darauf hin, dab die untersuchten Gesteine im Zuge kollisions-tektonischer Prozesse gebildet wurden. Die untersuchten peraluminösen Gesteine folgen einem kalkalkalischen Trend. Die Haupt- und Spurenelementverteilungen belegen eine fraktionierte Kristallisation des Fanos-Granites. Einfache Mischungsmodell-Berechnungen, die mittels der Hauptelemente erstellt wurden, ergeben eine 32 %ige Kristallakkumulation von vorwiegend Plagioklas, Kalifeldspat und Biotit. Eine Zweistufenmodell-Berechnung ergab eine 21- beziehungsweise 14 %ige Kristallakkumulation für die erste und zweite Stufe.

K/Ar mineral geochronology of the northern part of the Sithonia Plutonic Complex (Chalkidiki, Greece): implications for its thermal history and geodynamic interpretation

Abstract New K/Ar mineral ages of thirty nine samples (biotite, muscovite, K-feldspar) from the two-mica granodiorite to granite and leucogranite of the northern part of the Sithonia Plutonic Complex (Chalkidiki, Greece) are given in the present study. These data along with existing Rb/Sr mica and U/Pb zircon ages are used to investigate the thermal history of the plutonic complex and shed light on the process that affected it, and caused discordant Rb/Sr and K/Ar mineral ages. The K/Ar mineral dating yielded ages ranging from 38 to 49 Ma for muscovites, 32 to 47 Ma for biotites and 37 to 43 Ma for K-feldspars, respectively. The comparison of the K/Ar, Rb/Sr and U/Pb mineral ages and the closure temperatures of the different isotopic systems for the different minerals indicate a rapid cooling rate for the Sithonia pluton. The latter supports the hypothesis that the pluton was formed in a post orogenic extensional regime. Moreover, the K/Ar mineral isochrones indicate that a reheating of the pluton took place before 37 Ma and partially rejuvenated the K/Ar and Rb/Sr isotopic system of the minerals