Crystals characterized by oscillatory zoning show evidence for a quasi-cyclic alternation in the chemical composition of discrete growth-shells from tens of nanometers to tens of micrometers in thickness. Oscillatory zoning is most commonly observed and studied in crystals of magmatic plagioclase, but sensitive imaging techniques (e.g., Nomarski interference contrast microscopy, cathodoluminescence, back-scattered electron imaging, X-ray topographs) reveal its presence in many other minerals. Through the application of these techniques and an exhaustive review of the literature, oscillatory zoning is shown to occur in at least 75 rock-forming and accessory minerals comprising most major mineral classes: silicates (hydrous and anhydrous), sulfides, oxides, halides, carbonates, phosphates, and sulfates. Such mineral zoning is a common but often well-concealed phenomenon in magmatic rocks (particularly alkaline ones), hydrothermally altered rocks, mineralized rocks, and carbonate sequences. Mechanisms of oscillatory zoning are discussed, including the less-studied effects of adsorption and elastic stress in near-surface growth-layers. Its "non-equilibrium chemistry" makes oscillatory zoning a rich subject for further research.

Oscillatory zoning in minerals; a common phenomenon

Usually it is assumed that the partitioning of trace elements into titanite in metaluminous granitoid plutonic environments takes place under equilibrium conditions and that compositional zoning is due solely to progressive changes in melt chemistry and/or mineral/melt partition coefficients. Examination of titanites from a variety of Caledonian metaluminous granitoids and related rocks has revealed that sector zoning is present, indicating disequilibrium partitioning. The sector zoning in titanites is defined principally by the distribution of the rare earth elements (REE), Y, Nb, Al and Fe. The REE, Y and Nb preferentially occur within the minor (100) sectors relative to the morphologically important (111) sectors. The reverse is true of Al and Fe which preferentially occur within the (111) sectors relative to the (100) sectors. The patterns of sector zoning are complicated by the fact that the relative growth rates of the various crystal faces fluctuated during growth. Sector zoning indicates that crystal-interface kinetics are responsible for the observed patterns of element partitioning. It is concluded that differences in the lateral-layerspreading rates of crystal faces bring about the sector zoning. The results have implications for the use of trace element partition coefficients in the modelling of fractionation processes.

Kinetically induced compositional zoning in titanite: implications for accessory-phase/melt partitioning of trace elements

This paper describes structural models of four pyrophyllite edge faces: {010}, { 110}, { 100}, and { 130}. Water molecules chemisorbed to Lewis acid sites stabilize edge faces both crystallochemically and electrostatically. The detailed assignment of protons to surface oxygens and the orientation of OH bond-vectors both influence the surface Coulomb energy. The geometry chosen for the electrostatic calculations was infinite pyrophyllite ribbon the thickness of a single phyllosilicate layer and the width of 50 to 70 unit cells. Such a phyllosilicate ribbon has only two edges, a top and bottom, which were simulated using the edge-face models mentioned above. About 94% of the surface Coulomb energy is confined to the edge-face repeat unit. The surface Coulomb energies of the four edge faces are on the order of 2-3 n J/m, varying + 1 nJ/m with proton assignment. The Coulomb potential, measured either within the layer or parallel to the layer, has a distinct negative trend near the edge face that can be traced to chemisorbed water molecules. Finally, the correlation between proton Coulomb potentials at the edge face and the coordination environment of the protons is poor, obscured by long-range interactions.

The Surface Coulomb Energy And Proton Coulomb Potentials Of Pyrophyllite {010}, {110}, {100}, and {130} EDGES

Transmission electron microscopy (TEM) observation shows narrow regions in a Ti-containing Mg-rich annite of composition (K (sub 0.90) Na (sub 0.02) ) (Mg (sub 0.72) Fe (super 2+) (sub 1.78) Mn (sub 0.03) Ti (sub 0.27) Al (sub 0.05) ) (Si (sub 2.77) Al (sub 1.23) ) O 10 (OH,F) 2 from a granitic rock, where the + or -60 degrees and 180 degrees stacking angles occur extensively. These regions are a few hundreds of nanometers thick along the [001] (super *) direction and are within 1M or 2M 1 annite. The stacking sequence in one of these regions was determined by two atomic-resolution images recorded along [110] and [010] of the same crystal. Stacking sequences with + or -120 degrees or 180 degrees rotations are dominant, although those with + or -60 degrees rotations occur also. Locally 2O and more complex sequences exist. Compositional analysis by TEM indicated no difference in the chemical compositions between these regions and the adjacent ones with regular 1M or 2M 1 stacking sequence. The origin of these unusual stacking sequences in annite is discussed.

https://hal.univ-lorraine.fr/hal-01715541/document

First Occurrence of a Stacking Sequence Including (±60°, 180°) Rotations in Mg-Rich Annite

High temperature solution growth of perovskite Pb2CoWO6 single crystals

Hydrothermal growth of OH-phlogopite single crystals

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Hydrothermal growth of OH-phlogopite single crystals