Towards Zn-dominant Tourmaline : a Case of Zn-rich 2 Fluor-Elbaite and Elbaite from the Julianna System at 3 Piława Górna , Lower Silesia , SW Poland 4

Tourmalines are a group of minerals which may concentrate various accessory 16 components, e.g. Cu, Ni, Zn, Bi, Ti, Sn. The paper presents fluor-elbaite and elbaite from a dyke of 17 the Julianna pegmatitic system at Piława Górna, at the NE margin of the Bohemian Massif, SW 18 Poland, containing up to 6.32 and 7.37 wt.% ZnO, respectively. Such high amounts of ZnO are 19 almost two times higher than in the second most Zn-enriched tourmaline known to date. The 20 compositions of the Zn-rich tourmalines from Piława Górna, studied by electron microprobe and 21 Raman spectroscopy, correspond to the formulae: 22 (Na0.73Ca0.010.25)Σ1(Al1.03Li0.79Zn0.76Fe2+0.33Mn0.09)Σ3Al6B3Si6O27(OH)3(F0.66OH0.34), and 23 (Na0.78Ca0.010.21)Σ1(Al1.06Li0.87Zn0.88Fe2+0.10Mn0.09)Σ3Al6B3Si6O27(OH)3(OH0.84F0.16), respectively, with Zn 24 as one of the main octahedral occupants. A comparison with other tourmalines and associated 25 Zn-rich fluor-elbaite and elbaite from the pegmatite indicates that atypically high Zn-enrichment is 26 not a result of Zn-Fe fractionation, but dissolution and reprecipitation induced by a late 27 (Na,Li,B,F)-bearing fluid within the assemblage of gahnite spinel and primary schorl-type 28 tourmaline. This strongly suggests Na-Li-B-F metasomatism of gahnite-bearing mineral 29 assemblages as that is the only environment that can promote crystallization of a hypothetical 30 Zn-dominant tourmaline. The compositions of the Zn-rich fluor-elbaite and elbaite suggest three 31 possible end-members for such a hypothetical tourmaline species: NaZn3Al6B3Si6O27(OH)3(OH), 32 (Zn2Al)Al6B3Si6O27(OH)3(OH) and Na(Zn2Al)Al6B3Si6O27(OH)3O. 33

In this paper, we describe fluor-elbaite and elbaite with almost 7.5 wt.% ZnO from the Julianna system of anatectic pegmatites at Piława Górna, Góry Sowie Block, SW Poland.We discuss their chemistry, propose possible explanations for such high Zn enrichment and suggest the most probable environments for formation of even more Zn-rich crystals.
Dating of Julianna pegmatites gave an emplacement age of 377.6 ± 1.3 Ma [U-Th-Pb; monazite-(Ce)] and 380.7 ± 2.4 Ma (U-Pb-Th; uraninite) [19,26].These ages point to their formation by the anatectic melting of the metasedimentary-metavolcanic GSB rocks during tectonic exhumation at 385-370 Ma [27][28][29].Recent studies of trace elements in quartz from the Julianna pegmatites and their host rocks comply with this model and suggest that the pegmatite-forming melt was most probably generated at pressures ~5 kbar, at a slightly greater depth than the present day exposure level [30].The geochemical diversity of the metasedimentary-metavolcanic protolith, similar to paragneisses and amphibolites exposed in the Piława Górna quarry, is a plausible source for highly enriched partial melts with hybrid NYF + LCT characteristics.

Occurrence
The pegmatite dyke with the Zn-rich tourmaline was exposed in the Piława quarry in 2010, when it could be observed along a few tens of meters in horizontal section with a maximum thickness of ~3-4 m.The dyke showed typical zoning, and the assemblage of accessory minerals position it as transitional between NYF-and LCT-type pegmatites.Fan-shaped aggregates of muscovite, a few centimeters in length, in the graphic zone are a characteristic feature of this pegmatite.Short prismatic crystals of light-grey-bluish beryl, up to 5 cm long, occur together with quartz in interstices among feldspar crystals in the blocky feldspar zone and in the quartz core [18].
The blocky feldspar zone and the quartz core contain also up to 7 cm long intergrowths and radial aggregates of black tourmaline, up to 4-5 cm large quartz-garnet (almandine-spessartine series) symplectitic intergrowths, a few centimeter sized books of pale greenish muscovite, relatively abundant cassiterite (up to 3 cm large) and columbite-group minerals (up to 4 cm in length), as well as subordinate a few millimeter sized dark greenish crystals of gahnite.Lithium-bearing tourmalines were found only occasionally in the form of small, up to 2 cm long, dark green crystals within the books of greenish K-mica.Electron microprobe studies of the collected material reveal also the probably also cookeite and chamosite.Zinc-rich tourmaline was found only along the contact between adjacent gahnite and primary schorl-type tourmaline evolving to secondary fluor-elbaite.

Electron microprobe analysis (EMPA)
Electron microprobe analyses of tourmalines were performed at the Inter-Institute Analytical For analyses showing OH + F > 4 apfu due to excesses of microprobe determined SiO2 (quartz nanoinclusions), the amount of the component was reduced to a value for which the stoichiometric OH + F = 4 apfu was achieved, i.e. the highest content accepted for the tourmaline structure.

Raman spectroscopy
Raman spectra were collected in back-scattered geometry at the Faculty of Materials Science and Ceramics, AGH UST, Cracow, Poland, with a Horiba Labram HR spectrometer integrated with an Olympus BX 40 confocal microscope equipped with a Nd: YAG, 532 nm (10mW) laser and 1800 gr/mm grating.The spectra were recorded in the range 4000-50 cm -1 on randomly oriented surfaces of crystals mounted in epoxy resin in a 1-inch disc that was used also for EMPA studies.The Raman measurements were carried out with an estimated analytical spot size of ~1 µm, the microscope magnification 100×, an acquisition time of 600 s and accumulation of 2 scans.Calibration was done using the 520.7 cm -1 line of Si.

Primary tourmalines
The only tourmalines discernible by naked eye in hand specimens are a few centimetres large, black, and sometimes radially intergrown crystals of primary schorl (Trm I).Compared to its Trm IB precursor, it has generally higher, though partly overlapping Mn/(Mn+Fe) ratio of 0.080-0.183,similar or slightly higher contents of Al (up to 7.07 apfu) and Mn (0.09-0.17 apfu), a noticeable increase of Zn (0.06-0.14 apfu; up to 1.17 wt.% ZnO), decrease of Fe (down to 0.70 apfu)

Secondary dark greenish fluor-elbaite in muscovite books
Dark greenish translucent Li-tourmaline (Trm IIB) occurs as extremely rare, though relatively large, euhedral crystals up to 2 cm in length and 0.  Secondary Trm III contains sometimes relics of the primary tourmaline and numerous inclusions of mainly quartz and albite, sometimes gahnite, and very rarely sphalerite.The extent of Mn-Fe fractionation also increases from Trm IIIA to Trm IIIB, with Mn/(Mn+Fe) ranging from 0.17 to 0.29 and from 0.29 to 0.52, respectively.However, because Zn fractionates along with Mn, the ratio (Mn+Zn)/(Mn+Zn+Fe+Mg) is a better fractionation index yielding, respectively, 0.43-0.74and 0.81-0.93.32]; Fig. 3).In the range of OH stretching vibration modes (3400-3700 cm -1 ), the spectrum of Zn-rich Trm IIIA has three intense peaks with the maxima at 3498, 3561 and 3596 cm -1 (Fig. 5b).Peaks with similar Raman shifts in the spectrum of fluor-elbaite (3494 ± 8, 3562 ± 4 and 3593 ± 4 cm -1 ) were related by Watenphul et al. [29] to the most probable variants of configurations of the octahedral cations in fluor-elbaite:    The W OH group is bonded to three Y occupants.The presence of Al, Fe* 2+ and Li at the Y site of the described Zn-rich fluor-elbaite results in 8 allowed models of the YYY triad (LiLiLi and LiLiFe* 2+ local arrangements are not allowed because local anion bond valence requirements around the W=O(1) site would not be satisfied [34]).It should be expected that, with the small proportion of W OH in the total OH content (< 25 %), the abundances of individual YYY arrangements would be subordinate and the resulting intensities of the respective stretching vibration bands should be low.

Compositional relationships
Therefore they only have the potential to modify the basic pattern of the spectrum configured essentially by V OH bands.Applying to the YYY cationic arrangements the same reasoning as the one used above for the YZZ triad, it can be observed that the strongest effect of shifting the electron density away from the  In the case of an absence of Na or Ca at the X site (i.e. the presence of X-site vacancy as e.g. in foitite species), Watenphul et al. [32; Fig. 5] observed a few subordinate bands at wavenumbers generally above 3600 cm -1 .They assigned them to stretching vibrations in W OH groups bonded to YYY triad and associated with unoccupied X site (YYY-X ).Although we generally agree with this interpretation, we propose a slightly different assignment of some individual bands.The X-site vacancy is a result of a common substitution in the tourmaline structure:  + Me 3+ → X Na+ + Y Me 2+ .
In this substitution, Me 3+ cation replaces for Me 2+ in one octahedron of the Y triad.This means that the only valid YYY cationic arrangements in the structure of various tourmaline species with vacancy at the X site are: As a consequence, weak peaks with Raman shifts at 3630, 3544 and 3671 cm -1 in the spectrum of primary schorl-type tourmaline Trm IB can be interpreted as caused by the Y Fe* 2+Y Al Y Al-X , Y Fe* 2+Y Fe* 2+Y Al-X  and Y Li Y Fe* 2+Y Al-X  arrangements, respectively, as was proposed by Watenphul et al. [32].However, the bands are almost invisible in the spectra of Zn-bearing fluor-elbaite Trm IIIA, although the EMPA data suggest that X site in this tourmaline is similarly not fully occupied (Table 3).We interpret it as an indication that X  is essentially connected  The Zn-rich tourmaline (Trm III) from the Julianna system of anatectic pegmatites at Piława Górna is fluor-elbaite and elbaite with a composition close to Na(LiAlZn)Al6B3Si6O27(OH)3F, where Zn can be partly replaced by Fe 2+ and Mn 2+ (Zn >> Fe > Mn).Sokolov et al. [15], described a Zn-bearing tourmaline with a Zn content about half that from Piława Górna, and suggested the possible end-member composition NaZn3Al6B3Si6O27(OH)3(OH) for a hypothetical Zn-tourmaline.
However, two other hypothetical end-members are also possible: (Zn2Al)Al6B3Si6O27(OH)3(OH) and Na(Zn2Al)Al6B3Si6O27(OH)3O.In order to discuss the possibility of the existence of natural Zn-tourmaline two issues should be considered: (1) whether Zn alone or Zn + 0.5Al could dominate the Y site, and (2) which anion might be expected to be dominant at the W site of this tourmaline.
Zinc is only a very subordinate incompatible component of silicate magmas, and its lithophile affinity is restricted by the presence of sulphide species.Geochemical fractionation leads to the enrichment of granitic melts, particularly peralkaline magmas, in Zn and favours crystallization of gahnite as a minor accessory mineral in peraluminous leucogranites, pegmatitic granites and granitic pegmatites, as well as incorporation of traces of Zn into crystal structures of some primary phosphates, e.g.triphylite, lithiophilite, sarcopside or graftonite-group minerals [35].Lithophile behaviour of Zn in the Piława Górna pegmatitic system is evidenced by the crystallization of accessory Zn-bearing ilmenite-pyrophanite and gahnite in moderately fractionated dykes, and the assemblage of gahnite, Zn-bearing ferronigerite and zinconigerite, as well as genthelvine and Zn-bearing helvine in highly-fractionated ones.
In tourmaline-supergroup minerals, Zn is an accessory component commonly occurring in amounts up to a few tenths of ZnO wt.%.Such low concentrations indicate that Zn only slightly fractionates versus Fe in the tourmaline structure.In the Piława Górna pegmatites, even tourmalines from highly-fractionated dykes only occasionally have more than 1 wt.%ZnO.This fact suggests that hypothetical Zn-dominant tourmaline will rather not form due to Zn-Fe fractionation even in geochemically highly-evolved environments.Thus, it seems that the only specific mechanism that gadolinite-group minerals, hellandite-(Y), keiviite-(Y), pilawite-(Y), allanite-group minerals, xenotime-(Y), and monazite-(Ce).Highly fractionated pods with the LCT-type mineralization contain, among others, 'zinnwaldite', 'lepidolite', a Cs-bearing dark mica, spodumene, pollucite,

Figure 1 .
Figure 1.Simplified geological map of the Góry Sowie Block with the location of the Piława Górna quarry (after Szuszkiewicz et al. [16]).

5. 4 .
Zn-rich tourmaline from gahnite dissolution -fluor-elbaite + elbaite reprecipitation zonesZn-rich tourmaline (Trm III) was found as a secondary phase in a metasomatically altered assemblage of adjacent Trm IB (oxy-schorl to fluor-schorl) and gahnite.Highly-fractionated pale greenish gahnite with composition Zn(Al1.98Fe3+ 0.02)O4 [Zn/(Zn+Fe) = 0.965(3)], typically occurs as fractured crystals, up to a few hundred micrometers in size, that are partly overgrown by Trm III (Fig.2).Trm IB is usually largely dissolved and replaced by Trm IIIA (Zn-rich fluor-elbaite), forming clearly zoned crystals up to 1 millimeter in size (Fig.2).Compositional maps (Fig.3) present elemental distribution of Fe, Mn, Zn and Al in two areas, in which Zn-enriched tourmaline was detected.In both cases Fe concentration decreases gradually, coupled with increasing Zn and Al from the centre of the zoned crystals outwards (i.e. from Trm IB to Trm IIIA) and towards the adjacent gahnite.A local increase in Mn content in Trm IIIA is also marked.Trm IIIB (Zn-rich elbaite) occurs only as tiny domains, with the highest Zn concentration marked in Fig.3(Zn) as yellowish points within the greenish Zn-bearing matrix.The Zn-rich fluor-elbaite and elbaite appear only along the gahnite margins as a discontinuous zone with a maximum thickness of ~100 μm.

Figure 3 .
Figure 3. Fe-, Mn-, Zn-and Al-mapping for two occurrences of Zn-rich tourmaline (compare with Fig. 2).Color scale of increasing concentrations of the elements: dark blue-blue-green-yellow -orange-red-purple-white.

Figure 4 Figure 4 .Figure 5
Figure 4 presents variations in concentration of the most important elements in the tourmalines as functions of Mn + Zn fractionation expressed by the ratio (Mn+Zn)/(Mn+Zn+Mg+Fe).Mafic elements, such as Mg, Fe 2+ and Ti display rather coherent decreasing trends (Figs 4a-c).While present as minor components in Trm IA, Mg and Ti disappear in Trm IB, and may be present only as traces in more fractionated Trm II and Trm III.Iron decreases rapidly from Trm IA to Trm IIB, reaching a relatively constant content of 0.70-0.75apfu.Trm III shows a further steady decrease down to 0.06 Fe apfu along with Mn + Zn fractionation.Calcium, a subordinate component in Ti-bearing Trm IA, decreases very rapidly to a trace level in Trm IB (Fig.4d).However, there is a weak increase in Trm IIA-IIB at the (Mn+Zn)/(Mn+Zn+Mg+Fe) of 0.30-0.40,followed by a regular decrease in more fractionated compositions.Zinc, Mn, Y Al, Na and F show, at least partly, opposite tendencies (Figs4e-i) .There is a sharp increase of Mn and Al contents in Trm I owing to Mn-Fe fractionation, as well as dehydroxylation and alkali-vacant substitutions:Al 3+ + O 2-→ Y (Fe,Mg) 2+ + OH -and Al 3+ +  → Y (Fe,Mg) 2+ + X Na + ,respectively.In Zn-poor Trm IIA and IIB both components fluctuate around values of 0.10-0.15Mn apfu and ~1.0-1.3Al apfu.The appearance of Li in tourmaline (from Trm IB to Trm III) changes the compositional relationships between Y Al and bivalent Y-site cations due to the coupled substitution Li + + Al 3+ + F -→ 2 Y Fe 2+ + W OH -at the Y and W sites.This leads to the crystallization of fluor-elbaite and elbaite (some compositions of Trm II).As a result, Al, Li and Fe 2+ + Mn + Zn become the only significant Y-site occupants in more fractionated tourmalines.Further compositional evolution is a result of local fluctuation among activities of these components, especially due to dissolution and reprecipitation caused by the (Na,Li,F,B)-enriched fluid, and Mn + Zn vs. Fe fractionation.With fractionation, zinc forms a well-defined increasing trend (Fig.4e), reaching 0.02 apfu (0.15 wt.% ZnO) in Trm IA, 0.06 apfu (0.48 wt.% ZnO) in Trm IB, 0.14 apfu (1.17 wt.% ZnO) in Trm IIA, and 0.11 apfu (0.93 wt.% ZnO) in Trm IIB.Dissolution of gahnite and primary tourmaline and crystallization of secondary Zn-rich Trm III are marked by a sharp increase of Zn content up to 6.32 wt.% ZnO (0.76 Zn apfu) in Trm IIIA and to 7.37 wt.% (0.88 Zn apfu) in Trm IIIB.The stage of atypically high enrichment in Zn in these tourmalines is clearly shown in the (Mn+Zn)/(Mn+Zn+Mg+Fe) vs. Mn/(Mn+Fe) plot (Fig.4j).These two parameters show a simple linear relationship in all tourmaline generations, in which the increasing content of Zn can be attributed only to geochemical fractionation.In the relatively less evolved tourmalines (Trm I-IIB), the maximum values of the two ratios are relatively low, less than 0.30 and 0.20 for (Mn+Zn)/(Mn+Zn+Mg+Fe) and Mn/(Mn+Fe), respectively.In Trm III adjacent to gahnite, Zn suddenly increases, which is marked by the interruption of the trend and a sudden jump of the (Mn+Zn)/(Mn+Zn+Mg+Fe) value to 0.5-0.7.However, the trend is back to normal at the stage of Trm IIIB crystallization, what suggests the dominance of Mn and Zn fractionation over dissolution-reprecipitation.Such behavior is synchronous with a distinct decrease in F activity, reflected in a gradual transition from the crystallization of fluor-elbaite (Trm IIIA) to elbaite (Trm IIIB) (Fig.4i).

and 2 Y
Li Z Al Z Al-Y Al Z Al Z Al, where Y Fe* 2+ denotes the total of all divalent Y-site occupants ( Y Fe* 2+ = Y Fe 2+ + Y Mn 2+ + Y Zn 2+ + Y Mg 2+ ).A visible small asymmetry of the peak 3498 cm -1 centered at ~3475 cm -1 could come from Y Fe* 2+Z Al Z Al-2 Y Al Z Al Z Al complexes of Y and Z octahedra in the interpretation of Watenphul et al. [32].

Figure 6 .
Figure 6.Representative Raman spectra of: (a) primary schorl-type tourmaline (Trm IB) and (b) Zn-rich fluor-elbaite (Trm IIIA) in the range of OH stretching vibrations.Line colours: black -the recorded spectrum, green -bands dominated by V OH stretching vibrations, orange -bands dominated by W OH stretching vibrations with Na at the X site (it is not shown in the specifications of the bands), blue -bands dominated by W OH stretching vibrations with vacancy at the X site, magenta -a baseline.Dotted line marks an unresolved band composed, most likely, from a few significant components.
The spectrum of Li,Al-bearing schorl-type tourmaline Trm IB, with three visible maxima in the range of Raman shift below 3600 cm -1 , is dominated by 3566 cm -1 absorption, interpreted as dominantly coming from stretching vibrations in the V OH-Y Fe* 2+Z Al Z Al arrangement, and a superimposed band 3547 cm -1 of lower intensity from W OH-Y Fe* 2+Y Fe* 2+Y Al arrangements.The two remaining maxima are related to V OH-Y Li Z Al Z Al (3601 cm -1 ) and a relatively wide unresolved band (3502 cm -1 ), which we interpret as a superposition of V OH-Y Al Z Al Z Al, W OH-Y Al Y Al Y Al and W OH-Y Fe* 2+Y Al Y Al bands.
with Y Al Y Al Y Al triad as a result of the aforementioned substitution in the primary Y Fe* 2+Y Al Y Al triad.The Y Al Y Al Y Al cationic arrangement shows the strongest effect of shifting the electron density away from the W O-H bond and is characterized by the strongest increase of the W O-H distance that weakens the W O-H bond.As a consequence, the resulting band should be located at a lower wavenumber in the spectrum compared to other valid YYY-X  arrangements.In our opinion, the absorption band related to the W OH-Y Al Y Al Y Al-X  arrangement is superimposed on the much more intensive V OH-Y Li Z Al Z Al band and therefore is not discernible in the spectra of both tourmalines.The band at 3676 cm -1 related to Y Li Y Fe* 2+Y Al-X  arrangements is the only of this group to appear in the spectrum of Zn-rich fluor-elbaite Trm IIIA.It can easily be explained as the three cations are the main Y-constituents in this tourmaline.
can promote crystallization of Zn-rich tourmaline is Na-Li-B-F metasomatism of a gahnite-bearing mineral assemblage.The Zn-rich fluor-elbaite + elbaite (Trm III) from Piława Górna are an example, where the local crystallization environment was controlled by dissolution of gahnite by aggressive (Na,Li,F,B)-bearing fluids.Crystallization of Zn-rich tourmaline was, however, limited to a relatively narrow 0.1-millimetre-sized zone around gahnite, which suggests low diffusion of Zn toward fluor-elbaite overgrowths.Therefore, single crystals of Zn-dominant tourmaline seem rather unlikely in nature and intergrowths of gahnite with Li-bearing tourmalines (Na-Li-B-F metasomatism around gahnite) might be the most favourable environment where zones/domains of Zn-dominant tourmaline could form.All known tourmalines with elevated Zn contents are elbaite or fluor-elbaite [9-15; present study].The excesses of Al over Li and high amounts of X-site vacancies or W O 2-could favour the formation of Zn-tourmaline with dominance of the end-members (Zn2Al)Al6B3Si6O27(OH)3(OH) or Na(Zn2Al)Al6B3Si6O27(OH)3O.However, Zn-rich fluor-elbaite with the presence of significant X-site vacancies or W O 2-could also be interpreted as a solid solution of NaZn3Al6B3Si6O27(OH)3(OH) tourmaline with fluor-elbaite + rossmanite or darrelhenryite end-members, as such a case is rather shown by Raman spectra of Zn-rich fluor-elbaite Trm III.This implies that fluorine, as a significant component of the Zn-rich tourmalines, should be intimately related to the fluor-elbaite constituent, and the W site in Zn-dominant tourmaline should rather be dominated by OH or O. 5. Conclusions Atypically high Zn enrichment in tourmaline is generally connected with certain elbaites and fluor-elbaites.The enrichment in Zn does not result from Zn-Fe fractionation, but rather from dissolution of gahnite by (Na,Li,F,B,Be)-bearing fluid and reprecipitation of Zn-bearing secondary fluor-elbaite or elbaite in the nearest neighborhood of the decomposing gahnite.As fluorine is incorporated into tourmaline by the fluor-elbaite component, three potential Zn-dominant end
5 cm in diameter.In spite of the differences in color and size, the crystals are compositionally close to Trm IIA, except that the most Fe-enriched domains with 8.24-7.39wt.%FeO(1.14-1.01Feapfu)are even more Al-enriched (up to 7.32 apfu) (Table2).With increasing Mn-Fe fractionation [Mn/(Mn+Fe) = 0.082-0.161],the Trm IIB shows a decrease of Fe down to 0.68 apfu, coupled with an increase of Al and Mn up to 7.32 apfu and 0.13 apfu, respectively.Simultaneously, the calculated Li content increases from 0.53 apfu to 0.88 apfu.The amounts of Mg and Ti are negligible and usually close to 0.02-0.04apfu and ~0.01 apfu, respectively.
The contents of Zn vary randomly (0.13-0.93 wt.% ZnO; 0.02-0.11Zn apfu), although generally increase in sectors with higher Mn-Fe fractionation degrees.With fluorine contents from 0.38 up to 0.59 apfu and W OH -<< WF -, Trm IIB classifies as fluor-elbaite.Only several Al-poorest and Fe-richest compositions, with lowest measured F and calculated Li contents and W O 2-> W F -+ W OH -, might be classified as Fe-bearing darrellhenryite [the end-member composition Na(LiAl2)Al6B3Si6O27(OH)3O].

Table 3 presents
representative analyses of primary tourmaline and both secondary Zn-rich tourmalines.The chemical compositions of Trm IB in the gahnite-tourmaline assemblages do not differ from a typical composition of primary schorl Trm IB (Table1).The Trm IIIA corresponds to fluor-elbaite with 0.54-0.66apfu F and contains 7.00-7.05apfu Al, 0.26-0.57apfu Fe and 0.08-0.11apfu Mn.The Trm IIIB, on the other hand, classifies as elbaite with 0.16-0.36apfu F and has higher contents of Al (7.04-7.15apfu), significantly lower concentrations of Fe (0.06-0.20 apfu) and similar amounts of Mn (0.05-0.10 apfu).Magnesium and Ti are below detection limits in both secondary tourmalines.Preprints (www.

Table 3 .
Representative compositions of tourmalines of the Zn-rich assemblage.
[32] bond would take place in the Y Al Y Al Y Al arrangement (associated with the Na-occupied X site), and the weakest for the Y Li Y Li Y Al and Y Li Y Fe* 2+Y Fe* 2+ triads.Consequently, the W O-H bond should be the weakest in case of the first-type triad, and the strongest for the two remaining YYY arrangements.All this considered, the mentioned asymmetry of the 3498 cm -1 band observed can be interpreted rather as a result of stretching vibrations with Raman frequency 3480 cm -1 in W OH group bonded to the Y Al Y Al Y Al arrangement associated with the Na-occupied X site, and not as generated by the arrangement Y Fe* 2+Z Al Z Al-2 Y Al Z Al Z Al as was previously assumed[32].Our interpretation is corroborated by the composition of fluor-elbaite (Trm IIIA), in which the Al content is always slightly higher than the calculated content of Li + Fe* 2+ (Table3), which implies the existence of such Y Al Y Al Y Al sequence.We relate an additional band at 3544 cm -1 with a low intensity to vibrations of W OH group bonded with the Y Fe 2+Y Fe 2+Y Al arrangement.