https://eps.mcgill.ca/~courses/c644/Biomineralization%20(2011)/Growth_Apatite_Calcite/Paquette_Reeder_1995_Surface_growth_mechanism_trace_elements_in%20calcite.pdf

Relationship between surface structure, growth mechanism, and trace element incorporation in calcite

https://www.ipgp.fr/~cartigny/2003-GCA-Cartignyetal.pdf

On the possibility of a kinetic fractionation of nitrogen stable isotopes during natural diamond growth

The crystal chemistry of a natural topaz [with OH/(OH + F) < 0.5] was reinvestigated by means of laser ablation inductively coupled plasma mass spectroscopy, single-crystal X-ray diffraction (at 298 K) and neutron diffraction (at 298 and 10 K), and polarized infrared spectroscopy to deÞ ne unambiguously the real symmetry of topaz, the location of the proton and its thermal displacement parameters at room and low temperatures, the hydrogen-bonding and the vibration modes (stretching and bending) of the OH dipole. X-ray and neutron structural reÞ nements allow us to infer that the crystal structure of natural topaz with OH/(OH + F) < 0.5 can be described with the Pbnm space group. Violating res ections, found in the previous investigations and in this study, are likely due to Renninger effect (double diffraction phenomenon). The nuclear density Fourier map shows that the proton is located at Wyckoff 8d position and the reÞ ned coordinates are: x = 0.495(2), y = 0.252(1), z = 0.1629(7). The O-H bond lies on the (010)-plane and forms an angle of about 28.9° with the c-axis. Neutron structural reÞ nements at 298 and 10 K show that the displacement ellipsoid of the proton is highly anisotropic. The H-bonding arrangement appears to be complex, with at least four potential H···O/F interactions (distances < 2.38 A). The topological conÞ guration of the O-H group described by the neutron structural reÞ nements is conÞ rmed by the infrared investigation: the OH stretching mode (at 3640 cm –1 ) has no component of vibration parallel to the b axis (i.e., the O-H direction is perpendicular to [010]). The OH bending mode (at 1161 cm –1 ) shows components along the three crystallographic axes, which appear to be more prominent along the a and b-axes. The possible distribution into the crystal structure of topaz of the minor/trace elements found (Na, Ca, Fe Cr, V, Ti, B), and the implied topological effects, is discussed.

/pdf/new-insight-into-crystal-chemistry-of-topaz-a-multi-40bwkb51ln.pdf

New insight into crystal chemistry of topaz: A multi-methodological study

The composition of topaz from different granites and greisen in
the Krusne Hory/Erzgebirge area was investigated using electron
microprobe analysis (EMPA) and Laser Ablation Inductively
Coupled Plasma Mass Spectrometry (LA-ICP-MS). All topaz grains
are rich in F (17.9-19.8 wt.%, 1.73-1.90 a.p.f.u.) and the most
important minor/trace elements are P, Ge and Ga. Contents of P
up to 1 wt.% P2O5 (0.025 a.p.f.u.) were found in topaz from the
strongly peraluminous P-rich magmatic systems at Podlesi.
Regardless of genetic type, topaz from granites typically
contains 50-100 ppm Ge. The greatest amounts (up to 204 ppm Ge)
were found in topaz from quartz-topaz-apatite greisen in
Krasno. In fractionated granites and greisens, topaz is
calculated to contain 23-87% of the bulk Ge content in the
rock. In contrast, topaz does not concentrate Ga. The Ga
content of topaz (typically 5-35 ppm in S-type granites, <10
ppm Ga in A-type granites) is usually smaller than the bulk Ga
content of the rock. In addition, up to 16 ppm Sc, 23 ppm Sn
and >400 ppm Fe may be present.

Topaz as an important host for Ge in granites and greisens

In order to define the cathodoluminescence (CL) properties of magmatic topaz and its relation with trace-element composition, we studied topaz phenocrysts from the Ary-Bulak ongonite massif, Russia using a wide array of analytical techniques. Scanning electron microscopy CL panchromatic images reveal strong variations, which define micrometre-scale euhedral growth textures. Several truncations of these growth textures occur in single grains implying multiple growth and resorption events. The CL spectra of both CL-bright and -dark domains have a major peak in the near-ultraviolet centred at 393 nm. Cathodoluminescence images taken after several minutes of electron bombardment show decreasing emission intensity. Electron microprobe analyses indicate high F concentrations (average OH/(OH + F) = 0.04 calculated by difference, 100 wt.% – total from electron probe microanalyses), consistent with what has been found previously in topaz-bearing granites, and the OH stretching vibration (∼3653 cm −1 ) was detected in Raman spectra. Laser ablation inductively-coupled plasma mass spectrometry traverses performed across the CL textures detected trace elements at ppm to thousands of ppm levels, including: Fe, Mn, Li, Be, B, P, Nb, Ta, W, Ti, Ga, light rare-earth elements, Th and U. Lithium, W, Nb and Ta appear to be correlated with CL intensity, suggesting a role for some of these elements in the activation of CL in topaz. In contrast, no clear correlation was found between CL intensity and F contents, despite the fact that the replacement of OH for F is known to affect the cell parameters of topaz.

/pdf/relation-between-cathodoluminescence-and-trace-element-2zsggsyzv8.pdf

Relation between cathodoluminescence and trace-element distribution of magmatic topaz from the Ary-Bulak massif, Russia

Trace element distributions in topaz [AlrSiOo(F,OH)r] single crystals display both sectoral and intrasectoral zoning of trace elements as a function of growth-surface structure. Differential interference contrast microscopy shows that the dominant { I l0} form exhibits large, polygonized, spiral gowth hillocks with four vicinal faces, each comprising an array of parallel growth steps. Cathodoluminescence microscopy and synchrotron X-ray fluorescence microanalysis show that during gowth trace elements (As, Fe, and Ti) were differentially incorporated into vicinal faces having symmetrically nonequivalent step orientations, producing intrasectoral zoning in the bulk crystal. Subsectors that formed from vicinal faces related by surface symmetry possess identical compositions. In all cases, there is precise correlation between surface microtopography and trace element distribution, demonstrating a surface-structural control of trace element incorporation. Concentrations of As in time-equivalent regions of different subsectors within the {ll0} growth sector differ by as much as 9:1. Ti and Fe also differ significantly. Similar intrasectoral zoning related to surface-growth step orientation occurs on spiral growth hillocks on the {010}, {001}, and {l I l} forms as well. Sectoral zoning is also present in the majority of samples examined. Differences in trace element concentrations between time-equivalent regions of symmetrically nonequivalent $owth sectors are large, up to 100: I for As and between 23:-l and 7:5 for Fe, Ti, Ga, Ge, and Nb. Trace elements proxy for major elements in the structure but possess differences that significantly affect their incorporation at the surface. Zoning patterns preserve a record of that effect. Arrays of growth steps migrating in nonequivalent directions on a given surface, as well as growth surfaces of nonequivalent crystal forms, differ in their detailed structure ofincorporation sites and can differentially incorporate trace elements into coeval regions within a single crystal. Therefore, no single value of the distribution coefficient of a trace element can be applied for all areas of the crystal surface during growth. This indicates that the value ofthe distribution coefficient is path-dependent and thus not governed by equilibrium. Moreover, nonequivalent growth step orientations exhibit differences in such kinetic properties as step spreading (growth) rate and degree ofcurvature.

/pdf/evidence-for-the-importance-of-growth-surface-structure-to-3c18dhylnu.pdf

Evidence for the importance of growth-surface structure to trace element incorporation in topaz

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Evidence for the importance of growth-surface structure to trace element incorporation in topaz