Nabesite, Na2BeSi4O10ž4H2O, a new mineral species from the IliŽmaussaq alkaline complex, South Greenland

Ole V Petersen, Gerald Giester, Franz Brandstätter, Gerhard Niedermayr

Veröffentlichungen: Beitrag in FachzeitschriftArtikelPeer Reviewed

Abstract

Nabesite is found in complex tugtupite-bearing albitites on the Kvanefjeld Plateau, in the northwesternmost part of the lliŽmaussaq alkaline complex, South Greenland. It occurs in cavities, covered with albite crystals, in association with gmelinite, neptunite, analcime, gonnardite, lovdarite, trona(?) and opal(?). Nabesite forms aggregates of thin platy crystals, in parallel or subparallel orientation, the individual crystals show the pinacoids {100}, {010}, {001}, and {111} and {111}, both sphenoids, and range in size from 0.05 × 0.5 × 0.5 to 0.2 × 5 × 5 mm. The mineral is colorless and transparent, it has a white streak, and the luster is vitreous. The Mohs hardness is 5-6, it is brittle and shows good cleavage on (110) and (001), and the fracture is uneven. Nabesite is biaxial negative with na = 1.499(1). nß = 1.507(1) and n? = 1.511(1), 2Va (measured) 65(5)°, 2Va (calculated) 70°, and has X = a, Y = c and Z = b. Dmeas = 2.16(2) g/cm3, Dcalc = 2.21 and 2.22 g/cm3 for V derived from powder and single-crystal diffraction data, respectively. Data from EMP, SEM-EDS and results of the refinement of the crystal structure gave: Na2O 13.8 K2O 0.34, BeO 6.26, CaO 0.13, SiO2 62.4, H2O 18.05, total 100.98 wt%. The ideal formula is Na2BeSi4O10ž4H2O. The strongest lines on the X-ray powder-diffraction pattern [d in A°(1)(hkl)] are: 6.11(80)(111). 5.97(100)(002), 3.09(70)(310), 3.06(50)(222) and 2.988(60)(311). The unit-cell parameters refined from the powder data are: a 9.722(1), b 10.142(1), c 12.030(1) A°, V 1186.2 A°3. The structure was determined by single-crystal X-ray diffraction. Nabesite crystallizes in the orthorhombic space-group P212121. a 9.748(1), b 10.133(1), c 11.954(2) A°. V 1180.8(2) A°3, Z = 4. A total of 5704 unique reflections (at 293 K) gave a final R1 factor of 0.028 (wR2 = 0.078). The [SiO4] tetrahedra form sheets consisting of a combination of 4- and 8- membered rings, which are interconnected via the [BeO4] tetrahedra (a spiro-5 arrangement as secondary building unit) to form a framework. Channels house octahedrally coordinated sodium atoms and H2O molecules with a well-established system of hydrogen bonds. Nabesite is a zeolite with a new type of framework; the framework density is 16.94 T/1000 A°3. Relationships to the crystal structure of weinebeneite are evident.
OriginalspracheEnglisch
Seiten (von - bis)173-181
Seitenumfang9
FachzeitschriftThe Canadian Mineralogist
Jahrgang40
Ausgabenummer1
PublikationsstatusVeröffentlicht - 2002

ÖFOS 2012

  • 1051 Geologie, Mineralogie

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