Mariakrite, [Ca4Al2(OH)12(H2O)4][Fe2S4], a new mineral, the first layered double hydroxide intercalated with dithioferrate (iron disulfide) chains

• DOI: 10.2138/am-2024-9624
• Publication Date: 2025-01-29T22:37:32Z
• Authors: Mikhail N. Murashko; Yevgeny Vapnik; Natalia S. Vlasenko; Oleg S. Vereshchagin; Yulia S. Shelukhina; Igor V. Pekov; Sergey N. Britvin

Abstract Mariakrite is a new mineral in the hydrotalcite supergroup, and member of novel family layered double hydroxides, or LDH. It first reported LDH with dithioferrate, [Fe3+S2]− role an interlayer anion, cementitious Ca-aluminate (AFm phase) intercalated sulfide, sulfide-intercalated completely solved crystal structure. was discovered late hydrothermal assemblages confined to pyrometamorphic lithologies Hatrurim Formation, Negev Desert on Israeli side Dead Sea. The forms saber-like crystals up 2 mm long, 0.1 wide 0.5 μm thick, residing millimeter-sized cavities within larnite-jasmundite-brownmillerite rock. Associated minerals are katoite, portlandite, kuzelite hydrocalumite. has purple-brown color semimetallic luster; transmitted light, it transparent green-grey. flexible elastic. Mohs hardness 3–3.5. Calculated density 2.005 g cm−3. In reflected exhibits extreme pleochroism, from grey red-purple. Anisotropy very strong. Reflectance values for 4 wavelengths recommended by IMA Commission ore mineralogy [in air, R1/R2, % (γ, nm)]: 5.0/5.2 (470), 6.3/2.3 (546), 6.7/1.8 (589), 6.6/17.6 (659). triclinic (pseudo-pseudomonoclinic pseudo-trigonal), space group P1¯, 5.7107(2), b 9.9952(4), c 10.9095(4) Å, α 98.678(3), β 90.100(3), γ 90.019(3) °, V 615.58(4) Å3, Z = 1. 7 strongest lines X-ray powder diffraction pattern [d Å (I)(hkl)]: 10.83(100)(001), 9.90(39)(010), 5.42(75)(002), 3.96(22)(0− 22), 3.523(19)(−112), 2.856(37)(130), 2.400(23)(132). structure, refined R1 0.045 2379 independent observed reflections, consists hydrocalumite-type layers [Ca2Al(OH)6(H2O)2]+ iron disulfide chains. latter composed edge-sharing tetrahedra [FeS4] forming dithioferrate (III) [Fe3+S2]−. hydrocalumite-like sulfide chains linked via system O–H···S hydrogen bonds. Chemical composition (electron microprobe, wt.%, H2O based structural data) is: CaO 27.75, K2O 1.85, Al2O3 13.93, Fe 14.23, S 16.94, 23.88, Total 98.58. empirical formula calculated basis Σ(Ca,K,Al,Fe,S) 12 apfu (Ca3.73K0.30)Σ4.03Al2.06(OH)12.18Fe1.92S3.99·3.91H2O, corresponding ideal [Ca4Al2(OH)12(H2O)4][Fe2S4]. example which have no contacts cations anions, being suspended between hydroxide Therefore, might represent near-ideal model study physical chemical properties isolated quasi-one-dimensional