Naslov
Titanium and iron poor zincohoegbomite-16H, Zn14(Al, Fe3+, Ti, Mg)8Al24O62(OH)2, from Nezilovo, Macedonia: occurrence and crystal structure of a new polysome

Autori
Armbruster, Thomas ; Bermanec, Vladimir ; Zebec, Vladimir ; Oberhaensli, Roland

Izvornik
Schweizerische Mineralogische und Petrographische Mitteilungen (0036-7699) 78 (1998), 3; 469-477

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
zincohoegbomite-16H; crystal chemistry; X-ray single-crystal structure refinement; Nežilovo; Macedonia

Sažetak
The new polysome zincohoegbomite-16H, Zn14(Al, Fe3+, Ti, Mg)8Al24O62(OH)2, (space group P63mc, Z=1, a=5.729(2), c=37.097(5) A ; dcalc=4.52 g/cm3) occuring as smallplates in pink marbles at Nežilovo, Macedonia, is a mineral of the hoegbomite group. The hexagonal plates exhibit parallel intergrowth or occur in aggregates up to 2mm in size. The transparent orange mineral shows a pale yellow streak and has adamantine luster. Zincohoegbomite-16H is optically uniaxial negative (ored=1.850 and oyellow=1.845, e=not determined), pleochroitic: o - brown-yellow, e - pale greenish-yellow, Mohs hardness 6-7, neither cleavage nor parthing were observed. Zincohoegbomite-16H is a metamorphic reaction product in the high grade mrtsamorphic assemblage of the marbles at Nežilovo (Macedonia): it coexists with gahnite and zinc-rich phlogopite. The crystal structure of zincohoegbomite-16H was solved and refined from X-ray single-crystaldata to R=2.42% with 79 variables and 518 observations >4sigma(F). The new poysome has a close packed oxygen array composed of 16 oxygen layers stacked along the c-axis in the sequence ABCABCBACBACBABC. The oxygen array consists of cubic close packed subunits (complete gahnite-spinel blocks of six layers) with intercalated units of the hexagonal close packed type. Out of 15 cation sites seven are tetrahedrally (T) and eight are octahedrally (M) coordinated ; taking into account their multiplicities the formula T14M32O62(OH)2 can be derived. The tetrahedra are mainly occupied by Zn, whereas Al, Fe, and Ti have octahedral coordination.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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