Syntetyczny krzemian Pb i Sn z wykopalisk archeologicznych

Zofia Skrzat




Using X-ray diffraction techniques to identify polycrystalline beads from archaeological excavations at Gruczno, a similarity was noted between their powder data and those of colusite and famatinite given by L. G. Berry land R. M. Thompson. The similarity of powder patterns was also confirmed by a direct comparison of powder films, made under the same conditions, of the bead samples of colusite from Silver Bow County (USA) and of luzonite (end member of luzonite-famatinite series) from Cerro de Pasco (Peru). It should, however, be noted that considerable differences exist in intensity of some equivalent lines of the three samples. The powder patterns of the beads were indexed assuming, on calculations, that, this is a cubic system, and the unit cell dimensions a = 10.66 Å. Thus the unit cell dimensions are approximate to those of famatinite (10.67 Å) and colusite (10.61 Å). In spite of the geometrical resemblance of the powder patterns there is a fundamental difference in the chemical composition of these three substances. Both colusite and famatinite belong to sulphosalts. According to chemical analysis, (SiO2 - 17.92%, SnO2 - 7.14%, PbO - 73. 85%), the beads are silicates characterized by empirical formula - Pb7SnSi6O21 or, in another form - 6PbSiO3·PbSnO3. The measured density amounts to 5.76 g/cm3, the calculated being 5.68 g/cm3, Z = 2. For further investigations it is necessary to obtain monocrystalline specimens of this synthetic silicate.


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