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Fluor-schorl, a new member of the tourmaline supergroup, and new data on schorl from the cotype localities

Ertl, Andreas and Kolitsch, Uwe and Dyar, M. Darby and Meyer, Hans-Peter and Rossman, George R. and Henry, Darrell J. and Prem, Markus and Ludwig, Thomas and Nasdala, Lutz and Lengauer, Christian L. and Tillmanns, Ekkehart and Niedermayr, Gerhard (2016) Fluor-schorl, a new member of the tourmaline supergroup, and new data on schorl from the cotype localities. European Journal of Mineralogy, 28 (1). pp. 163-177. ISSN 0935-1221. doi:10.1127/ejm/2015/0027-2501.

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[img] Image (TIFF) (Figure S1 - Moessbauer spectrum (recorded at 295 K) of fluor-schorl from Zschorlau, Erzgebirge, Germany.) - Supplemental Material
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[img] Image (TIFF) (Figure S2 - Moessbauer spectrum (recorded at 295 K) of fluor-schorl from Johanngeorgenstadt, Erzgebirge, Germany.) - Supplemental Material
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[img] Image (TIFF) (Figure S3 - Moessbauer spectrum (recorded at 295 K) of schorl from Schneeberg, Erzgebirge, Germany.) - Supplemental Material
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[img] Image (TIFF) (Figure S4 - Moessbauer spectrum (recorded at 295 K) of schorl from Sauberg Mine, Ehrenfriedersdorf, Erzgebirge, Germany.) - Supplemental Material
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Fluor-schorl, NaFe^(2+) _3Al_6Si_6O_(18)(BO_3)_3(OH)_3F, is a new mineral species of the tourmaline supergroup from alluvial tin deposits near Steinberg, Zschorlau, Erzgebirge (Saxonian Ore Mountains), Saxony, Germany, and from pegmatites near Grasstein (area from Mittewald to Sachsenklemme), Trentino, South Tyrol, Italy. Fluor-schorl was formed as a pneumatolytic phase and in high-temperature hydrothermal veins in granitic pegmatites. Crystals are black (pale brownish to pale greyish-bluish, if <0.3 mm in diameter) with a bluish-white streak. Fluorschorl is brittle and has a Mohs hardness of 7; it is non fluorescent, has no observable parting and a poor/indistinct cleavage parallel to {0001}. It has a calculated density of ~3.23 g/cm^3. In plane-polarized light, it is pleochroic, O = brown to grey-brown (Zschorlau), blue (Grasstein), E = pale grey-brown (Zschorlau), cream (Grasstein). Fluor-schorl is uniaxial negative, ω = 1.660(2)–1.661(2), ɛ = 1.636(2)–1.637(2). The mineral is rhombohedral, space group R3m, ɑ = 16.005(2), c = 7.176(1) Å, V = 1591.9(4) Å^3 (Zschorlau), ɑ = 15.995(1), c = 7.166(1) Å, V = 1587.7(9) Å^3 (Grasstein), Z = 3. The eight strongest observed X-ray diffraction lines in the powder pattern [d in Å (I)hkl] are: 2.584(100)(051), 3.469(99)(012), 2.959(83)(122), 2.044(80)(152), 4.234(40)(211), 4.005(39)(220), 6.382(37)(101), 1.454(36)(514) (Grasstein). Analyses by a combination of electron microprobe, secondary-ion mass spectrometry (SIMS), Mössbauer spectroscopic data and crystal-structure refinement result in the structural formulae ^X(Na_(0.82)K_(0.01)Ca_(0.01)□_(0.16)) ^Y(Fe^(2+) _(2.30)Al_(0.38)Mg_(0.23)Li_(0.03)Mn^(2+) _(0.02)Zn_(0.01)□_(0.03))_(∑3.00) ^Z(Al_(5.80)Fe^(3+) _(0.10)Ti^(4+) 0.10) ^T(Si_(5.81)Al_(0.19)O_(18)) (BO_3)_3 ^V(OH)_3 ^W[F_(0.66)(OH)_(0.34)] (Zschorlau) and ^X(Na_(0.78)K_(0.01)□_(0.21)) ^Y(Fe^(2+)_(1.89)Al_(0.58)Fe^(3+)_(0.13)Mn^(2+)_(0.13)Ti^(4+)_(0.02)Mg_(0.02)Zn_(0.02)□_(0.21))_(∑3.00) ^Z(Al_(5.74)Fe^(3+)_(0.26)) ^T(Si_(5.90)Al_(0.10)O_(18)) (BO_3)_3 ^V(OH)_3 W[F_(0.76)(OH)_(0.24)] (Grasstein). Several additional, newly confirmed occurrences of fluor-schorl are reported. Fluor-schorl, ideally NaFe^(2+) _3Al_6Si_6O_(18)(BO_3)_3(OH)_3F, is related to end-member schorl by the substution F → (OH). The chemical compositions and refined crystal structures of several schorl samples from cotype localities for schorl (alluvial tin deposits and tin mines in the Erzgebirge, including Zschorlau) are also reported. The unit-cell parameters of schorl from these localities are slightly variable, ɑ = 15.98–15.99, c = 7.15–7.16 Å, corresponding to structural formulae ranging from ~^X(Na_(0.5)□_(0.5)) ^Y(Fe^(2+) _(1.8)Al_(0.9)Mg_(0.2)□_(0.1)) ^Z(Al_(5.8)Fe^(3+) _(0.1)Ti^(4+) _(0.1)) ^T(Si_(5.7)Al_(0.3)O_(18)) (BO_3)_3 ^V(OH)_3 ^W[(OH)_(0.9)F_(0.1)] to ~^X(Na_(0.7)□_(0.3)) ^Y(Fe^(2+) _(2.1)Al_(0.7)Mg_(0.1)□_(0.1)) ^Z(Al_(5.9)Fe^(3+) _(0.1)) ^T(Si_(5.8)Al_(0.2)O_(18)) (BO_3)_3 ^V(OH)_3 ^W[(OH)_(0.6)F_(0.4)]. The investigated tourmalines from the Erzgebirge show that there exists a complete fluor-schorl–schorl solid-solution series. For all studied tourmaline samples, a distinct inverse correlation was observed between the X–O2 distance (which reflects the mean ionic radius of the X-site occupants) and the F content (r^2 = 0.92). A strong positive correlation was found to exist between the F content and the <Y–O> distance (r^2 = 0.93). This correlation indicates that Fe^(2+)-rich tourmalines from the investigated localities clearly tend to have a F-rich or F-dominant composition. A further strong positive correlation (r^2 = 0.82) exists between the refined F content and the Y–W (F,OH) distance, and the latter may be used to quickly estimate the F content.

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Dyar, M. Darby0000-0003-4272-793X
Rossman, George R.0000-0002-4571-6884
Additional Information:© 2015 E. Schweizerbart'sche Verlagsbuchhandlung Science Publishers. Received 31 May 2015. Modified version received 12 August 2015. Accepted 18 August 2015. Published online 7 October 2015. Open Access Article Special issue dedicated to Thomas Armbruster. We thank Jürgen Tschiedel (from Aue, Saxony, Germany; till 1953 "Geologengehilfe" in the Zschorlau mine, which was closed in 1956) for helpful information about the historical dumps at Am Steinberg, Zschorlau, Saxony, Germany. Further we thank Matthias Kreibich ("Besucherbergwerk Zinngrube Ehrenfriedersdorf"), Wolfgang Barsch ("Besucherbergwerk Vereinigt Zwitterfeld zu Zinnwald"), Gerhard and Alexandra Voges (Neufahrn bei Freising, Bayern, Germany) for tourmaline samples from the Erzgebirge, Saxony, Germany. Special thanks for helpful information and references to Stadtverwaltung Ehrenfriedersdorf (Archiv), Germany, and to Zschorlauer Gemeindeverwaltung, Zschorlau, Germany. We also thank Kurt Folie, Meran, Trentino-South Tyrol, Italy, and Matthias Hanke, Ottobeuren, Germany, for providing tourmaline samples from Trentino-South Tyrol and Andreas Wagner, Vienna, Austria, for preparing the samples. Joachim Gröbner, Clausthal, kindly provided tourmaline samples from the Erzgebirge; Lars Epple, Gerlingen, Germany, and Herbert Kaiser, Maria Enzersdorf, Austria, samples from the Erongo Region. Franz Brandstätter, Naturhistorisches Museum, Wien, is thanked for semiquantitative analyses, Jan Cempírek, now Moravské Zemské Muzeum, Brno, Czech Republic, for a sample from Nedvědice, and Conrad Linde, Jena, Germany, for the sample from Nejdek. We sincerely thank John M. Hughes and Peter Bačík for constructive comments on this manuscript. This work was supported in part by Austrian Science Fund (FWF) project no. P23012-N19 and no. P26903-N19 to AE, by NASA grant NNG04GG12G to MDD and NSF grant EAR-0337816 to GRR.
Funding AgencyGrant Number
FWF Der WissenschaftsfondsP23012-N19
FWF Der WissenschaftsfondsP26903-N19
Subject Keywords:fluor-schorl; schorl; new mineral; Erzgebirge; type locality; Zschorlau; Grasstein; crystal structure; chemical composition; tourmaline
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Record Number:CaltechAUTHORS:20160413-073250515
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Official Citation:Andreas Ertl, Uwe Kolitsch, M. Darby Dyar, Hans-Peter Meyer, George R. Rossman, Darrell J. Henry, Markus Prem, Thomas Ludwig, Lutz Nasdala, Christian L. Lengauer, Ekkehart Tillmanns, and Gerhard Niedermayr Fluor-schorl, a new member of the tourmaline supergroup, and new data on schorl from the cotype localities Eur J Mineral, March 2016, v. 28, p. 163-177, First published on October 8, 2015, doi:10.1127/ejm/2015/0027-2501
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:66097
Deposited By: Ruth Sustaita
Deposited On:13 Apr 2016 18:08
Last Modified:10 Nov 2021 23:53

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