Molybdophyllite: crystal chemistry, crystal structure, OD character and modular relationships with britvinite
- Autor(en)
- Uwe Kolitsch, Stefano Merlino, D Holtstam
- Abstrakt
A detailed crystal-chemical study of the complex layered silicate molybdophyllite was conducted usingsingle-crystal X-ray diffraction (XRD) methods, supplemented by powder XRD, infrared (IR) andRaman spectroscopic studies, chemical analyses by energy-dispersive spectrometry (EDS) on ascanning electron microscope (SEM), and electron probe microanalysis (EPMA). The results, based onseveral samples from both La˚ngban and Harstigen, Filipstad, Sweden, show that the crystal structure ofmolybdophyllite has an order-disorder (OD) character. The latter is especially evident in specimensfrom La˚ngban which display a complex diffraction pattern characterized by the simultaneous presenceof sharp spots, diffuse reflections and continuous streaks. The sharp reflections define the unit cell ofthe family structure (a = 3.124, c = 41.832 A˚ , space group R32). Two main polytypes (maximumdegree of order structures) are indicated by the OD approach: a trigonal one and a monoclinic one; thelatter polytype is the most common in the samples that were studied and has space group C2, with a =16.232(6), b = 9.373(2), c = 14.060(3) A ˚ , b = 97.36(4)º and V = 2121.5(10) A ˚ 3.The crystal structure determination [R1 = 0.096], together with the EPMA, IR and Raman data,reveal that molybdophyllite is built up by a regular alternation of complex layers with a composition{Mg9[Si10O28(OH)8][OPb4]2}6+ and simple layers with a composition [(CO3)3×H2O]6_, leading to theideal crystal-chemical formula Pb8Mg9[Si10O28(OH)8[O2](CO3)3]×H2O (Z = 2).This contribution is mainly devoted to the results obtained for molybdophyllite sensu stricto, butnew data for britvinite [i.e. ‘molybdophyllite-18 A ˚ ’] are also presented and its modular relationshipwith molybdophyllite is discussed.
- Organisation(en)
- Institut für Mineralogie und Kristallographie
- Externe Organisation(en)
- Università degli Studi di Pisa, Swedish Museum of Natural History
- Journal
- Mineralogical Magazine
- Band
- 76
- Seiten
- 493-512
- Anzahl der Seiten
- 10
- ISSN
- 0026-461X
- Publikationsdatum
- 2012
- Peer-reviewed
- Ja
- ÖFOS 2012
- 105113 Kristallographie, 104006 Festkörperchemie, 105116 Mineralogie
- Link zum Portal
- https://ucrisportal.univie.ac.at/de/publications/ee0bf974-9cb4-4806-8053-efa7d94b8cd6