Gurimite, Ba3(VO4)2 and hexacelsian, BaAl2Si2O8 – two new minerals from schorlomite-rich paralava of the Hatrurim Complex, Negev Desert, Israel. (2nd January 2018)

• Record Type: Journal Article
• Authors: Galuskina, Irina O.; Galuskin, Evgeny V.; Vapnik, Yevgeny; Prusik, Krystian; Stasiak, Marta; Dzierżanowski, Piotr; Murashko, Mikhail
• Is Part Of: Mineralogical magazine. Volume 81:Number 4(2017)
• Page Start: 1009
• Page End: 1019
• Publication Date: 2018-01-02
• Subjects: gurimite, -- hexacelsian, -- electron back-scattered diffraction method, -- Raman, -- schorlomite-rich paralava, -- Negev Desert, -- Israel; Mineralogy -- Periodicals; Mineralogy -- Great Britain -- Periodicals; 549.05
• DOI: 10.1180/minmag.2016.080.147
• Languages: English
• ISSNs: 0026-461X

Abstract

Abstract: Two new barium-bearing minerals: gurimite, Ba3 (VO4 )2 (IMA2013-032) and hexacelsian, BaAl2 Si2 O8 (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 hexacelsian. 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, 1.945 and 1.561, respectively, were also calculated using the empirical formulas and the Gladstone-Dale relationship. The minerals are uniaxial and nonpleochroic. The following empirical crystal chemical formulae were assigned to holotype gurimite: (Ba2.794 K0.092 Ca0.084 Na0.033 Sr0.017 )∑3.020 (V1.827 5+ S0.091 6+ P0.051 5+ Al0.040 Si0.005 Fe0.005 3+ )∑2.017 O8, and holotype hexacelsian: (Ba0.911 K0.059 Ca0.042 Na0.010 )∑1.022 Al1.891 Fe0.072 3+ Si2.034 O8 . The Raman spectrum of hexacelsian is similar to the one of the synthetic disordered β-BaAl2 Si2 O8 . The Raman spectrum of gurimite is identical to that of synthetic Ba3 (VO4 )2 . The electron back-scattered diffraction (EBSD) pattern of gurimite was fitted to the structure of its synthetic analogue with the cell parameters of R 3 m, a = 5.784(1), c = 21.132(1) Å, V = 612.2(2) Å 3, Z = 3, giving a mean angular deviation = 0.43° (good fit). The Raman spectra of hexacelsian and its EBSD pattern suggest that natural hexacelsian corresponds to disordered synthetic β-hexacelsian P 63 / mcm, a = 5.2920(4) Å, c = 15.557(2) Å, α = β = 90°, γ = 120°. 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.