Wakabayashilite, [(As,Sb)6S9][As4S5]: Crystal structure, pseudosymmetry, twinning, and revised chemical formula
-
Paola Bonazzi
,
Giulio I. Lampronti
Abstract
The crystal structure of the rare mineral wakabayashilite was solved by direct methods using intensity data collected from a twinned crystal. This study revealed that, in spite of the strong hexagonal pseudosymmetry, the structure is orthorhombic (space group Pna21) with ao = 25.262(1), bo = 14.563(1), co = 6.492(1) Å, and Vo = 2388.4(2) Å3. The refinement of an anisotropic model led to an R index of 6.08% for 3135 observed reflections [Fo > 4σ(Fo)] and 8.71% for all 4260 independent reflections. Wakabayashilite is twinned by reticular merohedry [twin plane (110)]. There are two structural units in the structure: (1) [M6S9] bundle-like chains running along the [001] axis, consisting of corner-sharing MS3 trigonal pyramids (M = As, Sb), and (2) rods of As4S5 cage-like molecules, located in the space between three bundles and held together by van der Waals forces. The crystal chemical formula was therefore revised according to the structural results, yielding [(As,Sb)6S9][As4S5] (Z = 4). Both the intramolecular As-S and As-As bond distances and those within the bundle-like units match closely the values commonly observed in the molecule-formed structures of other arsenic sulfides and those found in orpiment, respectively. To contribute to the understanding of the effects of light exposure on the structure of the arsenic sulfides, the crystal was exposed to filtered polychromatic light. The unit-cell parameters were measured after each exposure. The results showed that the As4S5 molecules do not undergo any transformations, as previously found by exposing uzonite to light.
© 2015 by Walter de Gruyter Berlin/Boston
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Artikel in diesem Heft
- A synthesis of systematic mineralogy
- Oxidation/alteration of pentlandite and pyrrhotite surfaces at pH 9.3: Part 1. Assignment of XPS spectra and chemical trends
- Oxidation of pentlandite and pyrrhotite surfaces at pH 9.3: Part 2. Effect of xanthates and dissolved oxygen
- X-ray Rietveld refinement and FTIR spectra of synthetic (Si,Ge)-richterites
- Influence of crystal chemistry on ideal plastic shear anisotropy in forsterite: First principle calculations
- High-temperature Mössbauer study of Fe-substituted mullite
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- Quartz exsolution in clinopyroxene is not proof of ultrahigh pressures: Evidence from eclogites from the Eastern Blue Ridge, Southern Appalachians, U.S.A.
- The visible and infrared spectral properties of jarosite and alunite
- Wakabayashilite, [(As,Sb)6S9][As4S5]: Crystal structure, pseudosymmetry, twinning, and revised chemical formula
- Compression of albite, NaAlSi3O8
- Effect of polymorphic transition on oxygen isotope fractionation between aragonite, calcite, and water: A low-temperature experimental study
- Effect of current density on the electron microprobe analysis of alkali aluminosilicate glasses
- A high-pressure polytypic transformation in type-I chlorite
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- Mazzite-Na, a new zeolite from Boron, California: Its description and crystal structure
- Low-temperature illitization of smectite in the late eocene and early oligocene of the Isle of Wight (Hampshire basin), U.K.
- First reported sedimentary occurrence of berlinite (AlPO4) in phosphate-bearing sediments from Cioclovina Cave, RomaniaComment
- Optical and near infrared spectra of ringwoodite to 21.5 GPa: Implications for radiative heat transport in the mantle
- Letter. Observation of nano-clustered calcite growth via a transient phase mediated by organic polyanions: A close match for biomineralization
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