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Title: Chlorellestadite, Ca5(SiO4)1.5(SO4)1.5Cl, a new ellestadite- group mineral from the Shadil-Khokh volcano, South Ossetia
Authors: Środek, Dorota
Galuskina, Irina
Galuskin, Evgeny
Dulski, Mateusz
Książek, Maria
Kusz, Joachim
Gazeev, Victor
Keywords: Chlorellestadite; Crystal structure; New mineral; Raman; Shadil Khokh volcano; South Ossetia
Issue Date: 2018
Citation: Mineralogy and Petrology, Vol. 112, iss. 5 (2018), s. 743-752
Abstract: Chlorellestadite (IMA2017–013), ideally Ca5(SiO4)1.5(SO4)1.5Cl, the Cl-end member of the ellestadite group was discovered in a calcium-silicate xenolith in rhyodacite lava from the Shadil Khokh volcano, Greater Caucasus, South Ossetia. Chlorellestadite forms white, tinged with blue or green, elongate crystals up to 0.2–0.3 mm in length. Associated minerals include spurrite, larnite, chlormayenite, rondorfite, srebrodolskite, jasmundite and oldhamite. The empirical crystal chemical formula of the holotype specimen is Ca4.99Na0.01(SiO4)1.51(SO4)1.46(PO4)0.03(Cl0.61OH0.21F0.11)Σ0.93. Unit-cell parameters of chlorellestadite are: P63/m, a = 9.6002(2), c = 6.8692(2) Å, V = 548.27(3)Å3, Z = 2. Chlorellestadite has a Mohs hardness of 4–4.5 and a calculated density of 3.091 g/cm3. The cleavage is indistinct, and the mineral shows irregular fracture. The Raman spectrum of chlorellestadite is similar to the spectra of other ellestadite group minerals, with main bands located at 267 cm−1 (Ca–O vibrations), and between 471 and 630 cm−1 (SiO4 4− and SO4 2− bending vibrations) and 850–1150 cm−1 (SiO4 4− and SO4 2− stretching modes). Chlorellestadite forms in xenoliths of calcium-silicate composition when they are exposed to Cl-bearing volcanic exhalations at about 1000 °C under low pressure conditions.
Description: Acknowledgements This work was supported by grant no. 2015/17/N/ ST10/03141 (D. Ś.) from the National Science Centre (NCN) of Poland. Professor Pádhraig S. Kennan of University College at Dublin, Ireland, kindly helped with the English language. The authors are grateful to referee Professor S. Mills and Editor-in-Chief Dr. M.A.T.M. Broekmans for their constructive remarks, which greatly improved the original manuscript.
DOI: 10.1007/s00710-018-0571-1
ISSN: 0930-0708
Appears in Collections:Artykuły (WNP)

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