Clinopyroxene crystals

Hendricks, R. C. Dahl, P. S. (1987) Trace-element partitioning between coexisting metamorphic garnets and clinopyroxenes crystal field, compositional, and thermal controls. Geol. Soc. Amer., Ann. Meet., Abstr., 19, 700. 

Wood and Blundy (1997) adapted the lattice strain model to describe lanthanide partitioning between clinopyroxene and melt as a function of crystal composition, pressure and temperature. In developing the model, they arrived at relationships between and respectively, crystal composition, and pressure and temperature ... 

Landwehr et al. (2001) extended the model of Wood and Blundy (1997) to include and Th". They measured experimentally Aj and Z)xh in a wide variety of synthetic clinopyroxene compositions in order to evaluate the crystal compositional dependence of U-Th fractionation. Their observations confirm the predictions of Wood et al. (1999), namely that as the M2 site becomes smaller, so D-m becomes smaller than Du (Figs. 1 and 11). The M2 site becomes smaller as the enstatite component of the clinopyroxene increases and Ca on M2 is replaced by Mg. Enstatite solubility in clinopyroxene increases with increasing temperature, consequently clinopyroxene coexisting with orthopyroxene will show higher Du/Dih at higher temperature. For this reason, DuIDjb increases with increasing pressure along the mantle solidus, as discussed above. 

Fitting 71 Djh values (27 from their study and 44 from the literature) and subsequently excluding 5 outliers, Landwehr et al. (2001) derived the following expression for Th partitioning between clinopyroxene and silicate melt as a function of temperature, pressure, crystal chemistry and the molar MgMi partition coefficient ... 

Salters et al. (2002) have recently proposed an alternative expression for calculating D j and Dm in clinopyroxene as a function of crystal and melt composition. The expressions are calibrated on over 40 experimental determinations of Ehj and Dm- Salters et al. (2002) do not give values for the average absolute deviation. The full expressions (with 1 s.d. uncertainties in brackets) are ... 

ABSTRACT The aim of this study was to test portable infrared spectroscopy for non-destructive analysis of ancient construction mortar. Mortar samples from the House of the Vestals, in Pompeii, Italy, were initially examined with traditional analytical techniques, including X-ray fluorescence, X-ray diffraction and thin section analysis. These techniques were used to establish mineralogical and chemical profiles of the samples and to verify the results of experimental field methods. Results showed the lime-based binder was composed of calcite, and the volcanic sand aggregate contained clinopyroxene, plagioclase, sanidine and olivine crystals. 

This model of liquid extraction is symmetrical to fractional crystallization and has attracted renewed interest after the demonstration by Johnson et al. (1990) that REE distributions in abyssal peridotite clinopyroxene cannot be accounted for by equilibrium melting processes. The solid is supposed to maintain its chemical homogeneity while liquid is continuously extracted. Only the last drop of liquid is supposed to be in equilibrium with the residue. 

Pyroxenes are poly silicates ( inosilicates in the mineralogical classification), crystallizing, respectively, in the monoclinic clinopyroxenes spatial groups C2lc, Pljlc, P2ln) and orthorhombic systems orthopyroxenes spatial groups... 

Table 5.37 lists the various terms of the lattice energy of some clinopyroxene components. Data refer to the C2/c spatial group. Components Mg2Si206 and Fe2Si20g, which crystallize in Pljlc, must thus be considered fictitious. ... 

The Boina emission products show a more or less continuous differentiation trend from transitional basalt to pantellerite. In the nonperalkaline field, the transition from basalt to ferro-basalt is dominated first by olivine F > 0.65) and then by plagioclase F > 0.45), with minor clinopyroxene. A second differentiation step with the appearance of Fe-Ti oxide crystals begins at F = 0.45 Fe and Ti decrease abruptly. Less marked discontinuities are also observed at F = 0.3 (silica-oversaturated trachytes) and F = 0.15 (peralkalinity field). 

Dal Negro A., Carbonin S., Domeneghetti C, Molin G. M., Cundari A., and Piccirillo E. M. (1984). Crystal chemistry and evolution of the clinopyroxene in a suite of high pressure ultramafic nodules from the newer volcanism of Victoria, Australia. Contrib. Mineral. Petrol, 86 22N229. 

Ghose S., Kersten M., Langer K., Rossi G. and Ungaretti L. (1986). Crystal field spectra and Jahn-Teller effect of Mn in clinopyroxene and clinoamphiboles from India. Phys. Chem. Minerals, 13 291-305. 

Griffin W. L. and Mottana A. (1982). Crystal chemistry of clinopyroxenes form St. Marcel manganese deposit, Val d Aosta, Italy. Amer. Mineral, 67 568-586. 

Retrograde metamorphic processes, linked to hydrothermal fluid circulation, finally produced a new mineral assemblage constituted mainly by tremolite-actinolite> epidote + chlorite + quartz + sericite + titanite + hematite. The amphibole appears as green fibrous crystals over clinopyroxene and other anhydrous minerals. 

Clark, J. R., Appleman, D. E., and Papike, J. J. (1969). Crystal chemical characterisation of clinopyroxene based on eight new structure refinements. Miner. Soc. Amer. Sp. Papers 2, 31-50. 

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