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Mineralogical ClassificationIMA 2013-032 = gurimite; IMA 2015-045 = hexacelsian
27th Oct 2017 09:51 UTCMarco E. Ciriotti Manager
▪ Galuskina, I.O., Galuskin, E.V., Vapnik, Y., Prusik, K., Stasiak, M., Dzierżanowski, P., Murashko, M. (2017): Gurimite, Ba3(VO4)2, and hexacelsian, BaAl2Si2O8 – two new minerals from schorlomite-rich paralava of the Hatrurim Complex, Negev Desert, Israel. Mineralogical Magazine, 81, 1009-1019.
Abstract:
Two new barium-bearing minerals – gurimite, Ba3(VO4)2 (IMA2013-032) and hexacelsian, BaAl2Si2O8 (IMA2015-045) were discovered in veins of paralava cutting gehlenite-flamite hornfels located in the Gurim Anticline in the Negev Desert, Israel. Gurimite and hexacelsian occur in oval polymineralic inclusions in paralava and are associated with gehlenite, pseudowollastonite or wollastonite, rankinite, flamite, larnite, schorlomite, andradite, fluorapatite, fluorellestadite, kalsilite, cuspidine, aradite, zadovite and khesinite. Gurimite and hexacelsian form elongate crystals <10 μm thick. The minerals are colourless and transparent with a white streak and vitreous lustre, and have (0001) cleavage, respectively good in gurimite and very good in hexacelcian. Fracture is irregular. Density calculated using empirical formulas gave 5.044 g·cm-3 for gurimite and 3.305 g·cm-3 for hexacelsian. Mean refractive indexes, respectively, 1.945 and 1.561, were also calculated using the empirical formulas and the Dale-Gladstone relationship. The minerals are uniaxial and nonpleochroic. The following empirical crystal chemical formulae were assigned to holotype gurimite: (Ba2.794K0.092Ca0.084Na0.033Sr0.017)Σ3.020(V5+1.827S6+0.091P50.051Al0.040Si0.005Fe3+ 0.005)Σ2.017O8, and holotype hexacelsian: (Ba0.911K0.059Ca0.042Na0.010)Σ1.022Al1.891Fe3+ 0.072Si2.034O8. Raman spectrum of hexacelsian is similar to the one of the synthetic disordered β-BaAl2Si2O8. The Raman spectrum of gurimite is identical to that of synthetic Ba3(VO4)2. The EBSD pattern of gurimite was fitted to the structure of its synthetic analogue with the cell parameters of R3m, a = 5.784(1), c = 21.132(1) Å, V = 612.2(2) Å3, Z = 3, giving a mean angular deviation = 0.43º (good fit). The Raman spectra of hexacelsian and its EBSD pattern suggest that natural hexacelsian corresponds to disordered synthetic β-hexacelsian P63/mcm, a = 5.2920(4) Å, c = 15.557(2) Å, α = β = 90º, γ = 120º. We suggest that after relatively fast crystallization of the main constituents of the paralava, gurimite, hexacelsian and also other Ba-bearing phases crystallized from residual melt enriched in incompatible elements that filled interstices between crystals of the main constituents.
28th Oct 2017 09:05 UTCHans Kloster
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Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2024, except where stated. Most political location boundaries are © OpenStreetMap contributors. Mindat.org relies on the contributions of thousands of members and supporters. Founded in 2000 by Jolyon Ralph.
Privacy Policy - Terms & Conditions - Contact Us / DMCA issues - Report a bug/vulnerability Current server date and time: April 19, 2024 04:32:06