ISSN:
1432-0967
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Geologie und Paläontologie
Notizen:
Abstract A coarse-grained, colourless lepidolite from a pegmatite of the Elba Island (Italy) has been examined. X-ray powder-diffraction and single-crystal patterns reveal the presence of the 1M and 2M2 polymorphs, for wich cell parameters are given. On the basis of the optical and X-ray data the same composition for both the polymorphs is inferred. From the chemical analysis data of the whole micaceous material the following formula has been computed: (Ca0,01Na0,06K0,92Rb0,06) (Al1,27Mg0,01Li1,75) (Si3,36Al0,64)O10 (F1,53OH0,47). The crystal structure of this mica has been studied by means of one-dimensional Fourier projections on c* and several interesting structural parameters were derived. Among them the mean tetrahedral rotation results to be about 11° for both the polymorphs: a value (quite similar to those of the other trioctahedral micas with K+ as interlayer cation) wich does not confirm Radoslovich's hypothesis that lepidolites should have a symmetry of the tetrahedral layers very close to the perfect hexagonality. Finally a new hypothesis on the structure of the 2M2 polymorph consistent with such a proved ditrigonal symmetry of the basal oxygens arrangement in the lepidolites is pointed out.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF00371536
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