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Coupled Substitutions in Schorl-Dravite Tourmaline: New Evidence from SE Ireland
Abstract
Analyses of tourmaline and coexisting muscovite in tourmaline-bearing rocks from SE Ireland indicate that the content of Si in tourmaline is not fixed but is dependent on bulk chemistry, varying inversely with A1. Zoning patterns within tourmaline reflect this and, despite theoretical objections, substitution of Si by A1 in the tetrahedral site must occur in nature. Ti may also substitute for Si. Ca and Ti are generally involved in a coupled substitution. Estimates of the degree of alkali-defect and proton-loss substitution in SE Ireland tourmalines indicate that the former process is at least as important as the latter and that bulk chemistry is important in determining which substitution occurs. The general importance of alkali-defect substitution and AI ~-Si suggests that the most useful way to treat microprobe data for schorl-dravite tourmalines is to assume the presence of 3B and 4(OH) and calculate on the basis of 24.5 oxygen atoms.
... In past, many researchers worked on the nomenclature (Dietrich, 1985;Hawthorne and Henry, 1999;Henry et al., 2011;Novak et al., 2009), crystal structure/chemistry, and substitution mechanism of tourmaline (Ertl et al., 2018;Foit and Rosenberg, 1977;Gallagher, 1988;MacDonald and Hawthorne, 1995). Dravite, a magnesium-rich alkali tourmaline, occurs mainly in metamorphic and metasedimentary rocks, especially in metapelites to metapsammites, amphibole gneisses, marbles, dolomites, and skarns (Bacik et al., 2012). ...
... Foit and Rosenberg (1977) recommended that the charge imbalance due to the presence of Al in the Y-site is more effectively maintained by alkali defect and proton-loss coupled substitutions. On plotting the composition of tourmaline in (R 1+ + R 2+ ) -R 3+ diagram (after Gallagher, 1988), the tourmalines fall on the right side near the junction of alkali deficiency and proton loss trend lines suggesting very low alkali deficiency and proton loss defined by the exchange vector (Mg, Fe)(OH) Al − 1 O − 1 in the studied tourmaline (Fig. 12a). On plotting the composition in X□ -Al plot with exchange vectors, AlOMg − 1 (OH) − 1 , and Al X Mg − 1 Na − 1 , the analyzed tourmaline follows the dravite -oxy-dravite line defined by exchange vector AlOMg − 1 (OH) − 1 (Fig. 12b). ...
Tourmaline of rare elbaite-dravite series has been reported for the first time from the sapphire bearing pegmatite from the Paddar area, Kishtwar District (Jammu and Kashmir), India. The sapphire-bearing pegmatites are hosted by ultramafic rocks of the Higher Himalayan Crystalline metamorphic complex. These pegmatites are dominantly composed of sodic-plagioclase, perthite, tourmaline, and sapphire, whereas microcline, biotite, and muscovite make up the minor phases. The tourmaline from these pegmatites contains high Mg, Ca, Na, and F content as well as low K, Fe, and Cr content. They are classified as alkali tourmaline, characterized by higher Mg/Mg + Fe and Na/Na + Ca ratios. They display complex substitution mechanisms during the crystallization (Li + Al↔Mg, Fe↔Mg, Na↔Ca, B + Al↔Si) and post crystallization alteration by the hydrothermal fluids. The geochemistry of tourmaline suggests that the tourmaline is crystallized from peraluminous, silicious pegmatitic melt (enriched in Al, Li, B, and H2O). This melt was most likely formed through partial melting of the metasediments of Higher Himalaya Crystalline during the M2 phase of regional metamorphism. The pegmatitic melt was injected in the ultramafics, resulting in bimtasomatism reaction evidenced by the development of systematic alteration zones next to the contact. Bimetasomatism results in the diffusion of the Ca and Mg from host rock to pegmatitic melt, and removal of silica from the pegmatitic melt, which leads to the increase of Al in pegmatitic melt. Finally, a saturation of the Al in the melt with a high Mg influx from host rock results in the favourable environment for crystallization of Mg-rich tourmaline and sapphire.
... The metasomatism of sediments commonly forms tourmalines by boron-rich hydrothermal fluids (Slack 1980). The chemistry of the tourmalines is also partly dependent on the bulk chemistry of the original sediments, where tourmalines grown in an Al-rich environment preferentially having high Al contents (Gallagher 1988). Replacement of original metamorphic and igneous minerals assemblages with boron enriched assemblages is a common feature of country rocks immediately adjacent to pegmatite. ...
Saïda clays formation “Argile de Saïda” is one of the main sedimentary series of the Upper Jurassic of Northwestern Algeria. It was first defined in the western part of the Tlemcenian domain. This domain is situated between the Tellian Atlas in the north and the high plateaux Oranaises in the south. The study area constitutes the eastern extremity of the Tlemcenian domain in the Djebel Brame section (Northwestern Algeria). It is represented by an interbedded clay and sandstone alternation of Upper Jurassic age, which is rich in foraminifera. The taxonomic study of the samples shows a population of foraminifera consisting of 28 species belonging to10 genera, 08 families and 04 suborders divided into three associations, largely dominated by the Nodosariidae. Paleoenvironmental interpretations based on the foraminiferal data and geochemical (calcimetry) analyses indicate a shallowing of the basin during the Upper Oxfordian.
... The metasomatism of sediments commonly forms tourmalines by boron-rich hydrothermal fluids (Slack 1980). The chemistry of the tourmalines is also partly dependent on the bulk chemistry of the original sediments, where tourmalines grown in an Al-rich environment preferentially having high Al contents (Gallagher 1988). Replacement of original metamorphic and igneous minerals assemblages with boron enriched assemblages is a common feature of country rocks immediately adjacent to pegmatite. ...
The numerous processes (superficial and deep) occurring on margins, their origins, consequences, interactions and quantifications are only very partially described and understood. The identification of the relative role of factors is sometimes completely contradictory between authors. Here, we showed the results of a long-term multidecadal and multidisciplinary study (using geophysical, geological, stratigraphic, paleontological, geomorphologic, geochemical, microbiological and numerical models) in the Western Mediterranean Sea that acts as a natural laboratory at many different scales. We showed how sediments efficiently recorded at the same time: variations of glacio-eustatic sea-level changes, variations of sediments yield and sources, and also enabled quantifying vertical movements and geodynamic worldwide events but also detailed regional mass transport, turbidites and contourites deposits. They are also an archive of paleoclimatic, palaeoceanographic and diagenetic processes.
... The metasomatism of sediments commonly forms tourmalines by boron-rich hydrothermal fluids (Slack 1980). The chemistry of the tourmalines is also partly dependent on the bulk chemistry of the original sediments, where tourmalines grown in an Al-rich environment preferentially having high Al contents (Gallagher 1988). Replacement of original metamorphic and igneous minerals assemblages with boron enriched assemblages is a common feature of country rocks immediately adjacent to pegmatite. ...
The present work is focused on the distribution of landslides in Foglia River basin (central Italy), using a heuristic approach supported by GIS tools for the construction of statistical analysis and spatial data. It aims to investigate any dependencies and/or relationships between natural factors related to the study area and landslides. In the study area, 2821 landslides were surveyed covering a total area of 155 km² that corresponds to 22% of the entire basin. The findings of the study highlight the importance as well as the role of individual factors, such as lithology, land use, orientation, and slopes, which led to the development of landslides analyzed.
... The metasomatism of sediments commonly forms tourmalines by boron-rich hydrothermal fluids (Slack 1980). The chemistry of the tourmalines is also partly dependent on the bulk chemistry of the original sediments, where tourmalines grown in an Al-rich environment preferentially having high Al contents (Gallagher 1988). Replacement of original metamorphic and igneous minerals assemblages with boron enriched assemblages is a common feature of country rocks immediately adjacent to pegmatite. ...
The Algerian coastline stretches for 1622 km including a coastal area called Bejaia that measures 100 km in length. Bejaia is located on the east side with sandy beaches that attract tourists. This coastal fringe is subject to a remarkable decline. Several beaches are witnessing recession. In this respect, the study aims to estimate the average rates of erosion and accretion between the two coastal lineages (1989 and 2017), through a GIS on ArcGIS v 10.2 and its digital shoreline analysis system (DSAS) module. Erosion dominates most of the beaches of this coastal fringe. Measures should be urgently taken to preserve the natural heritage that is at the heart of our country.
... The metasomatism of sediments commonly forms tourmalines by boron-rich hydrothermal fluids (Slack 1980). The chemistry of the tourmalines is also partly dependent on the bulk chemistry of the original sediments, where tourmalines grown in an Al-rich environment preferentially having high Al contents (Gallagher 1988). Replacement of original metamorphic and igneous minerals assemblages with boron enriched assemblages is a common feature of country rocks immediately adjacent to pegmatite. ...
This edited book is based on the papers accepted for presentation during the 2nd Springer Conference of the Arabian Journal of Geosciences (CAJG-2), Tunisia, in 2019. Major subjects treated in the book include geomorphology, sedimentology, and geochemistry. The book presents an updated unique view in conjugating field studies and modeling to better quantify the process-product binomial unusual in geosciences. In the geomorphology section, 24 papers deal with topics related to fault slip and incision rates, soil science, landslides and debris flows, coastal processes, and geoarcheology, and geoheritage. Under the sedimentology section, 34 papers including stratigraphy, and environmental, tectonic, and diagenetic processes, together with evolutionary, biostratigraphic, and paleo-environmental significance of paleontology are presented. Additionally, this section also contains papers on marine geosciences, from molecular proxies related to climate to geophysical surveys. Last but not least, the third section on geochemistry is composed of 26 papers that are focused on sedimentary geochemistry and mineralogical characterization, magmatic and metamorphic processes and products, and the origin and exploration of mineral deposits. This book resumes the current situation related to the abovementioned topics mainly in the Mediterranean realm. The volume book is of interest to all researchers, practitioners, and students in the fields of geomorphology, sedimentology, and geochemistry, as well as those engaged in environmental geosciences, soil science, stratigraphy and paleontology, geoarcheology and geoheritage, marine geosciences, petrology, metallogenesis, and mineral deposits.
... The metasomatism of sediments commonly forms tourmalines by boron-rich hydrothermal fluids (Slack 1980). The chemistry of the tourmalines is also partly dependent on the bulk chemistry of the original sediments, where tourmalines grown in an Al-rich environment preferentially having high Al contents (Gallagher 1988). Replacement of original metamorphic and igneous minerals assemblages with boron enriched assemblages is a common feature of country rocks immediately adjacent to pegmatite. ...
Paleontological content of sedimentary phosphorites in El-Kouif locality, northeastern Algeria, was analyzed. Materials were concentrated by sample washing and outcrops surface collecting of friable phosphorites facies, yielding a multitude of phosphatised fish teeth rich in species of variable morphology, representing 15 species of Elasmobranchii (Euselachii and Batoidea). The fish fauna indicates tropical to temperate paleo-environmental conditions. Most of the species represent benthic/nektonic forms of coastal areas with neritic and midwater depths. This fish fauna confirms a Thanetian age for the phosphatic formation of El Kouif, highlighting the importance of fossil fish for the formation of sedimentary phosphorites. Apparently, this Thanetian assemblage occupied a relatively narrow gulf.
... Tourmaline could be found in a variety of geologic settings (i.e., in pegmatitic rocks, in hydrothermal quartz veins, in igneous and pyroclastic rocks, in metamorphic rocks resulted from regional metamorphism, and in sedimentary and diagenetic rocks due to digenetic process). The worldwide tourmaline is derived from boron-rich magmas, commonly characterized by peraluminous felsic composition (Wolf andLondon 1997, London 1999;Bosi et al. 2019a), or it is related to metasomatism for Al-rich sediments by boron-carrying fluids (Slack 1996, Gallagher 1988, Dutrow et al. 1999. Hence, tourmaline is commonly found in granite pegmatites and in their vicinity to hosting sedimentary rocks. ...
Tourmaline in Sikait area is closely associated with stratiform metapelites schistose rocks. The distribution of tourmaline is confined to the Nugrus shear zone, along with leucocratic rock varieties (leucogranite, pegmatite and aplite dykes). Tourmaline occurs either as disseminated isolated clusters of crystals or as discontinuous tourmalinite bands within the metapelites rocks, pegmatites or quartz veins. Four mineral assemblages have been identified at Sikait area on the approach to the pegmatite contact, viz: (1) Quartz-biotite-K-Feldspar-chlorite, which consists mainly of the original metamorphic silicate plus anomalously high amounts of modal tourmaline; (2) Quartz-biotite-tourmaline-chlorite; (3) Tourmaline-quartz-muscovite; and (4) Tourmaline-quartz. The variations in the mineral assemblages and whole-rock chemistry within the mineralized zones appear to be a function of boron metasomatism and potash leaching. The normalized rare earth elements (REE) patterns of samples from the four assemblages suggest a partial alteration of the original pelitic rock pattern by the metasomatized magmatic fluids. The metasomatic/alteration zones represent an episode of (B-, Li-, Rb-enriched fluid) during pegmatite fluid-schist interactions. The aqueous fluid from the pegmatite reacts with the schist breaking down sheet silicate for leaching of Rb, Li and K and forming tourmaline-rich assemblages.
... Tourmalinites are commonly formed by metasomatism of sediments by B-rich hydrothermal fluids (Slack, 1996). The chemistry of these tourmalines is also partly dependent on the bulk chemistry of the original sediments, with tourmalines growing in an Al-rich environment, preferentially having a high Al content (Gallagher, 1988). However, Al-Mg disorder between the Y and Z sites makes the assignment of cation site occupancies rich for Mg tourmaline (Grice and Ercit, 1993;Hawthorne et al, 1993). ...
The tourmaline-bearing quartz-rich pegmatites of granitic composition are intruded in the gneissic rocks of the Higher Himalayan Crystalline unit of the Proterozoic age. Tourmalines occur as disseminated grains that are typically black-colored and unzoned and show characteristic intergrowth with quartz along the rim. According to geochemical classification diagrams, tourmalines are classified to the alkali group and are named as Fe-rich dravite type due to their higher Mg content. The cationic ratios of Mg/Mg + Fe and Na/Na + Ca are very high, whereas Fe/Fe + Mg cationic ratios are low, indicating the poorly differentiated nature of pegmatites. Compositional variation in tourmaline is controlled by both homovalent and hetrovalent substitution, expressed by exchange vectors □Al2ONa-1R2+-2(OH)-1, □AlNa-1R2+-1, □(OH)Na-1O-1Ca(Fe, Mg)Na-1Al-1, AlO(R2+OH)-1, FeAl-1, and Fe-Mg-1. The parent melt of tourmaline was peraluminous in nature with high salinity and H2O. The detailed field characteristics, mineral association, texture of tourmaline, and chemical composition reveal that tourmaline crystallizes from a magmato-hydrothermal environment.Graphical abstract
Chromian tourmaline, a member of the dravite group, has been encountered in the Cr-bearing skarns occuring between the serpentinites and quartzites in the Outokumpu area, in association with chrome-bearing silicates ang oxides. The reported chromian tourmaline contains Cr2O3 9.60 %. The mineral is trigonal with a0 = 15.96 Å, c0 = 7.2d Å and D = 3.101 g/cm3. The chromian tourmaline is uniaxial, negative and very strongly pleochroic with ω = 1.687 and ε = 1.638.
A number of well-characterized silicate minerals and metal oxides have been analysed by the electron-probe technique in two different instruments with a range of accelerating potentials. Simple oxides and minerals have been used as standards for the elements Na to Ca and pure metals for the elements Ti to Ni.Factors affecting the accuracy of analysis are discussed in detail. The effect of wavelengthshift errors is treated in a general manner and curves enabling the magnitude of the effect to be determined in any instrument are given. Corrections associated with X-ray generation (the atomic number correction), absorption and secondary excitation by characteristic and continuous radiation are examined separately. It is shown that analyses with an accuracy of 1 per cent or better can be obtained with recently developed correction methods and it is suggested that this approach is now a workable and possibly a preferable alternative to methods employing empirical calibration.
The usefulness of tourmaline as a petrogenetic indicator in this setting and the internal evolution of this pegmatite are discussed. Major- and trace-element analyses for 29 tourmalines are tabulated.-J.A.Z.Inst. for Study of Mineral Deposits, South Dakota School of Mines & Technology, Rapid City, SD 57701-3995, USA.
Alkali-free tourmalines synthesized in the system MgO-AlrO.-SiOz-BzOs-HrO in the pres-ence of excess B2Os and HzO at I kbar have been characterized by optical and X-ray measurements, partial chemical analyses, and infrared spectra. Infrared absorption bands in the OH-stretching region are more similar to those of elbaite than dravite. Syn. Temp. Refractive Index ('C) e b) 600 r.605(l) 1.624(t) 450 1.607(l) 1.624(t) Cell Dimensions Partial Analysis (MoleTo) d(A) c(A) SiO, Al,O3 MeO 15.884(2) 7.128(t) 49.2 32.8 18.0 15.847(5) 7.108(3) 44.2 34.9 20.e Assuming stoichiometric boron, variables in site occupancies include numbers of (l) vacancies at alkali sites, (2) rvAl, (3) vIAl, and (4) protons. Although chemical data serve to constrain site occupancies only within broad limits, structural formulas are univariant in that determination of any one variable would fix the others. Comparison of cell parameters of alkali-free tourmaline with those of elbaite and dravite suggest approximate vI(Mg,/AI) ratios which correspond to the structural formulas: n o,rMgo.or(Mgr.eeAlr 0r)Al6(Siu srAlo 4r)(BOs)sOr?.'4(OH){ r. at 600"C I o o.Mgo.r.(Mg,.u2Alr.n")Al.(Si6.2aAl0 zzXBO')sO* uo(OH)r.no at 450'C Alkali site occupancy (t*Mg) and Al content are higher while the proton content is lower at 450'C than at 600'C. Alkali-free tourmaline synthesized at 600'C is an Al-rich, alkali-defective dravite.