Refikite from Krásno, Czech Republic: a crystal-and molecular-structure study

Abstract

The crystal structure of the organic mineral refikite has been determined. The mineral was found in joints in bark and wood from pine trees in the 'V Borkách' peat deposit near the town of Krásno, Slavkovský les Mountains, western Bohemia, Czech Republic. It forms white to light-yellow polycrystalline crusts or randomly intergrown, transparent, colourless, very thin, acicular crystals up to 0.2À0.5 mm long. Sometimes, colourless-to-white elongated prismatic crystals up to 1À1.5 mm in size were encountered. The mineral is soft (Mohs hardness~1) and very brittle, with an uneven fracture. No visible cleavage was discerned. Crystals have a greasy-to-glassy lustre; fine crystal aggregates have a pearly lustre. Refikite, empirical formula C 20 H 34 O 2 or C 19 H 33 COOH, is a derivative of abietic acid. It is orthorhombic, space group P2 1 2 1 2, with a = 22.6520(7), b = 10.3328(3), c = 7.6711(2) Å , V = 1795.49(9) Å 3 , Z = 4. Refikite comprises two closely related compounds based on perhydrophenanthrene. The major component has two axial methyl groups, one terminal carboxylic group and one terminal propan-2-yl (isopropyl) group joined to the three fused rings in the same fashion as in abietic acid. However, the fused ring system is fully reduced (contains single bonds only). In the minor component, the terminal propan-2-yl group is replaced by a propen-2-yl (methylvinyl) group. The crystal structure is stabilized by strong O_HÀO hydrogen bonds. High-resolution mass spectroscopy (HRMS) confirmed a molecular mass of 306 and the formula C 20 H 34 O 2 . Hydrogen-1 and carbon-13 nuclear magnetic resonance (NMR) spectroscopy showed the presence of four methyl groups in the major component; infrared (IR), Raman and NMR spectra are consistent with the structure. The HRMS, IR and Raman spectroscopy methods confirmed the presence of a minor component containing the propen-2-yl group replacing the propan-2-yl group. This is also reflected in a shortened C15ÀC17 single bond metric of 1.468(6) Å shown by single-crystal X-ray analysis. The trivial name of the major component of refikite is tetrahydroabietic acid or abietan-18-oic acid. This work represents the first proof of the existence of abietic acid derivatives as naturally occurring species.

Holubite, Ag3Pb6(Sb8Bi3)Σ11S24, from Kutná Hora, Czech Republic, a new member of the andorite branch of the lillianite homologous series

“…Structurally, holubite has a unit cell and symmetry similar to those of ramdohrite, fizélyite, Ag-rich fizélyite, uchucchacuaite, menchettiite, oscarkempffite (Makovicky and Topa, 2014) and lazerckerite, with a ≈ 19, b ≈ 13, c ≈ 8.5, β ≈ 90°, V ≈ 2200, (regardless of axial setting) and space group P 2 1 /n or P 2 1 /c . Lazerckerite, Ag 3.75 Pb 4.50 (Sb 7.75 Bi 4 )S 24 , is a new mineral of the andorite branch, of the lillianite homologous series with L % ≈ 90–95 and a Bi/(Bi+Sb) ratio of ~0.30 (IMA2022-113; Pažout et al 2023b). Chemically, holubite can be compared with other related lillianite homologues on the basis of two parameters: (1) lillianite substitution percentage L %; and (2) bismuth (vs. antimony) content expressed as the Bi/(Bi+Sb) ratio.…”

“…He has cooperated closely with archaeologists who made use of his vast knowledge in the field of medieval mining and metallurgy. The new mineral and its name have been approved by the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA2022-112; Pažout et al 2023a). Part of the co-type sample has been deposited in the collections of the Department of Mineralogy and Petrology, National Museum, Cirkusová 1740, 193 00 Praha 9, Czech Republic, under the catalogue number P1P 10/2022.…”

Tvrdýite, Fe2+Fe32+Al3(PO4)4(OH)5(OH2)4·2H2O, a new phosphate mineral from Krásno near Horní Slavkov, Czech Republic

“…Dr Tvrdý is the author of papers on the mineralogy and geology of the Krásno -Horní Slavkov area (e.g. Plášil and Tvrdý, 2008;Sejkora and Tvrdý, 2009) and surrounding occurrences (Sejkora et al, 2008;Tvrdý and Plášil, 2010;Pažout et al, 2015). The pronunciation of tvrdýite is /twe:(r) 'di: ait/, or using special characters /twɜːʳ ˈdiː aɪt/.…”