IMA 2015-102 = methathénardite

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Marco E. Ciriotti
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IMA 2015-102 = methathénardite

Messaggio da Marco E. Ciriotti » gio 07 nov, 2019 11:16

Prossima pubblicazione.

Referenza:
▪ Pekov, I.V., Shchipalkina, N.V., Zubkova, N.V., Gurzhiy, V.V., Agakhanov, A.A., Belakovskiy, D.I., Chukanov, N.V., Lykova, I.S., Vigasina, M.F., Koshlyakova, N.N., Sidorov, E.G., Giester, G. (2019): Alkali sulfates with aphthitalite-like structures from fumaroles of the Tolbachik Volcano, Kamchatka, Russia: I. Metathénardite, a natural high-temperature modification of Na2SO4. Canadian Mineralogist, 57, (in press).
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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Marco E. Ciriotti
Messaggi: 26138
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
Contatta:

Re: IMA 2015-102 = methathénardite

Messaggio da Marco E. Ciriotti » gio 21 nov, 2019 16:36

Referenza:
▪ Pekov, I.V., Shchipalkina, N.V., Zubkova, N.V., Gurzhiy, V.V., Agakhanov, A.A., Belakovskiy, D.I., Chukanov, N.V., Lykova, I.S., Vigasina, M.F., Koshlyakova, N.N., Sidorov, E.G., Giester, G. (2019): Alkali sulfates with aphthitalite-like structures from fumaroles of the Tolbachik Volcano, Kamchatka, Russia: I. Metathénardite, a natural high-temperature modification of Na2SO4. Canadian Mineralogist, 57, (in press).

Abstract:
A new mineral, metathénardite, ideally Na2SO4, the high-temperature hexagonal dimorph of thénardite, a natural analogue of the synthetic phase Na2SO4(I), was found in the sublimates of active fumaroles at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure eruption, Tolbachik volcano, Kamchatka, Russia. The holotype originates from the Glavnaya Tenoritovaya fumarole in which metathénardite is associated with hematite, tenorite, fluorophlogopite, sanidine, anhydrite, krasheninnikovite, vanthoffite, glauberite, johillerite, and lammerite. The cotypes 1 and 2 are from the Arsenarnaya (with hematite, tenorite, fluorophlogopite, sanidine, euchlorine, wulffite, anhydrite, fluoborite, johillerite, nickenichite, calciojohillerite, badalovite, tilasite, cassiterite, and pseudobrookite) and the Yadovitaya (with tenorite, euchlorine, fedotovite, dolerophanite, langbeinite, krasheninnikovite, anhydrite, and hematite) fumaroles, respectively. All specimens with metathénardite were collected from areas with temperatures of 350–400 °C. Metathénardite forms hexagonal tabular, lamellar, or dipyramidal crystals (forms: {001}, {100}, {102}, and {201}) up to 3 mm combined in crusts up to several hundred cm2 in area. The mineral is transparent to semitransparent, colorless, white, light-blue, greenish, yellowish, grayish or brownish, with vitreous luster. Dmeas. = 2.72(1), Dcalc. = 2.717 g/cm3. Metathénardite is optically uniaxial (–), ω = 1.489(2), ε = 1.486(2). The empirical formulae are (Na1.92K0.05Ca0.02Zn0.01)[S0.99O4] (holotype), (Na1.54K0.22Ca0.09Cu0.01Mg0.01)[S1.00O4] (cotype 1), and Na1.65K0.11Ca0.05Cu0.04Mg0.01)[S1.01O4] (cotype 2). Admixed K and bivalent cations probably stabilize the hexagonal aphthitalite-like structure of metathénardite at room temperature. The crystal structure was solved using single crystals of all three samples, R1 = 0.0852, 0.0452, and 0.0449 for holotype and cotypes 1 and 2, respectively. The space group is P63/mmc, and the unit-cell parameters of the holotype are a = 5.3467(9), c = 7.0876(16) Å, V = 157.47(6) Å3, and Z = 2. The strongest reflections of the powder X-ray diffraction pattern [d,Å(I)(hkl)] are: 4.667(27)(100), 3.904(89)(101), 3.565(33)(002), 2.824(94)(102), 2.686(100)(110), and 1.939(35)(202). Metathénardite and thénardite clearly differ from one another in X-ray diffraction data and infrared and Raman spectra.
Marco E. Ciriotti

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