New minerals with modular structure derived from hatrurite from the pyrometamorphic rocks. Part IV: Dargaite, BaCa12(SiO4)4(SO4)2O3, from Nahal Darga, Palestinian Autonomy. (21st May 2018)

• Record Type: Journal Article
• Authors: Galuskina, Irina O.; Gfeller, Frank; Galuskin, Evgeny V.; Armbruster, Thomas; Vapnik, Yevgeny; Dulski, Mateusz; Gardocki, Mariusz; Jeżak, Lidia; Murashko, Mikhail
• Is Part Of: Mineralogical magazine. Volume 83:Number 1(2019)
• Page Start: 81
• Page End: 88
• Publication Date: 2018-05-21
• Subjects: dargaite, -- arctite group, -- antiperovskite structure, -- Raman spectrum, -- pyrometamorphic rocks, -- Hatrurim Complex; Mineralogy -- Periodicals; Mineralogy -- Great Britain -- Periodicals; 549.05
• DOI: 10.1180/minmag.2017.081.095
• Languages: English
• ISSNs: 0026-461X

Abstract

Abstract: Dargaite, ideally BaCa12 (SiO4 )4 (SO4 )2 O3, is an additional member of the arctite group belonging to minerals with a modular intercalated antiperovskite structure derived from hatrurite. The holotype specimen was found at a small outcrop of larnite pseudoconglomerates in the Judean Mts, West Bank, Palestinian Autonomy. Larnite, fluorellestadite–fluorapatite, brownmillerite, fluormayenite–fluorkyuygenite and ye'elimite are the main minerals of the holotype specimen; ternesite, shulamitite and periclase are noted rarely. Dargaite, nabimusaite and gazeevite occur in linear zones with higher porosity within larnite rocks. Pores are filled with ettringite and Ca-hydrosilicates, less commonly with gibbsite, brucite, baryte, katoite and calciolangbeinite. Dargaite is colourless, transparent with a white streak and has a vitreous lustre. It exhibits pronounced parting and imperfect cleavage along (001). Mohs' hardness is ~4.5–5.5. The empirical formula is (Ba0.72 K0.24 Na0.04 )Σ1 (Ca11.95 Mg0.04 Na0.01 )Σ12 ([SiO4 ]0.91 [PO4 ]0.05 [AlO4 ]0.03 [Ti 4+ O4 ]0.01 )Σ4 ([SO4 ]0.84 [PO4 ]0.14 [CO3 ]0.02 )Σ2 (O2.54 F0.46 )Σ3 . Dargaite is trigonal R $\overline 3 $ m, the unit-cell parameters are: a = 7.1874(4) Å, c = 41.292(3) Å, V = 1847.32(19) Å 3 and Z = 3. The crystal structure of dargaite was refined from X-ray single-crystal data to R 1 = 3.79%. The calculated density is 3.235 g cm –3 . The following main Raman bands are distinguished on the holotype dargaite (cm –1 ): 122, 263, 323, 464, 523, 563, 641 and 644, 829 and 869, 947, 991 and 1116. The formation conditions of dargaite are linked to the local occurrence of pyrometamorphic by-products (gases, fluids and melts) transforming earlier mineral associations at ~900°C.