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 (SiO44− and SO42− bending vibrations) and 850–1150 cm−1 (SiO44− and SO42− 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.
Highlights
Chlorellestadite, ideally Ca5(SiO4)1.5(SO4)1.5Cl, was found in an altered calcium-silicate xenolith enclosed in rhyodacite lava fromEditorial handling: M
Recent study of Cl-bearing minerals in altered xenoliths from the Shadil-Khokh volcano revealed a Cl-dominant member of the ellestadite group
Chlorellestadite was initially identified as an unknown mineral by electron scanning microscope on polished sections prepared from several fist-sized xenolith samples that were collected during fieldwork in Summer 2012
Summary
Chlorellestadite, ideally Ca5(SiO4)1.5(SO4)1.5Cl, was found in an altered calcium-silicate xenolith enclosed in rhyodacite lava from. Fluorine in ellestadite from Crestmore, this mineral is hydroxylellestadite (Rouse and Dunn 1982). Chlorellestadite was described as an intermediate high-temperature phase in Portland clinker (Chen and Fang 1989; Saint-Jean and Hansen 2005) and was used as a synthetic phase for production of new technological materials (Fang et al 2011, 2014). Recent study of Cl-bearing minerals in altered xenoliths from the Shadil-Khokh volcano revealed a Cl-dominant member of the ellestadite group. This phase was investigated and the new mineral species chlorellestadite (IMA2017–013) was approved by the IMA Commission for New Minerals, Nomenclature and Classification – CNMNC in 2017. The type material of chlorellestadite is deposited in the mineralogical collection of the Fersman Mineralogical Museum, Leninskiy pr., 18/k2, 115,162 Moscow, Russia, under catalogue number 4975/1
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