| Bellbergite | |(K,Ba,Sr)2Sr2Ca2(Ca,Na)4(H2O)30| [Al18Si18O72] | ||
| Morphology: |  Bellbergite, Ettringer Bellerberg, Ettringen, Eifel, Germany. Width of image 1.5 mm. Bernd Ternes Collection. © Volker Betz |
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| Hexagonal Tiny (0.2 mm) columns of stacked dipyramidal crystals, commonly overgrown by levyne-Ca. |
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| Physical properties: | |||
| Cleavage: none Hardness: about 5. Density: 2.20 g/cm3 Luster: vitreous Streak: white |
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| Optical properties: | |||
| Color: colorless,
white Uniaxial (-). ω = 1.522, ε = 1.507, δ= 0.015 Dispersion: none |
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| Crystallography: | |||
| Space Group: P63/mmc, P63mc or P-62c | |||
| Unit cell: a = 13.244 Å c = 15.988 Å | |||
| Name: | |||
| Bellbergite was described and named by Rüdinger et al. (1993), as the natural occurrence of the synthetic zeolite EAB. It is a very rare zeolite that occurs in calc-silicate xenoliths in leucite tephrite of Bellberg volcano near Mayen, Eifel, Germany. The name is for the type locality. | |||
| Crystal structure: | |||
| The zeolite framework-type
EAB was solved by Meier and Groner (1981)
on crystals of synthetic Na, TMA EAB (Zeolite E of Aiello
and Barrer, 1970, made
with Na and tetramethyl-ammonium cations). Rüdinger et
al.
(1993) refined the structure of bellbergite, starting with the atom positions
of the EAB structure. The framework topology is based on stacking of
6-rings in the sequence ABBACC…. This topology consists of two
kinds of columns, one of gmelinite cages connected with the single 6-rings
(A) and the other of double 6-rings separated by eab cages
(see EAB).
Tetrahedra of the 6 rings show no regular ordering. Stacking faults are
possible with erionite or levyne structures, both of which have alternating
single and double 6-rings.
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| Non-framework cations and water molecules occur in both the gmelinite and eab cages. There are three positions (green in the drawing) for K in each gmelinite cage, where they are bonded to framework oxygens and water molecules. Two of these positions are in each unit cell, and may be occupied by Ba and Sr as well. One Ca site is located in the center of the single 6-ring between gmelinite cages. Two sites (red), occupied by Ca and Na, are located on the center line in the eab cage. Also on the center line are the two Sr sites located closer to the double 6-rings on each end. A water molecule (blue) is positioned in the center of the double 6-ring and six more (also blue) are located around the cations in the eab cage. | |||
| Chemical composition: | |
| The only analysis for bellbergite was given by Rüdinger et al. (1993). The TSi value is near 0.50, well lower than synthetic TMA-E, |(Me4N)2Na7(H2O)26|[Al9Si27O72] with the same structure (Aiello and Barrer, 1970). |