Gemstones from the ducal part of the fortified settlement of Poznań (10th/11th century) in the light of gemological studies and micro-Raman spectroscopy

Abstract

During archaeological excavations in Poznan there were discovered a ducal palace, a chapel dated to the 10th century, and goldsmith’s workshop adjacent to them. In the layer of ashes at the bottom of the manufacture, there were fragments of gold found together with numerous glass beads and gems. Fourteen gems, made of rock crystal, agate, carnelian, milky chalcedony, garnet, were chosen for gemstone analysis and micro-Raman spectroscopy. The study material is dominated by beads (12 samples, of which six is faceted and six globular), while two pyrope samples have the cabochon cut. It should be emphasized that the rock crystal gems in the collection are usually heptagonal. Majority of the Poznan collection is of high quality, which is a sign of an advanced grinding and faceting technology. Pyrope from the Poznan collection contains inclusions of apatite, rutile, quartz, and magnetite, identified with micro-Raman spectroscopy. A similar combination of inclusions was recognized in pyrope from deposits in Vestřev near Turnov (Bohemia), and hence it indicates that the artifacts from Poznan were made of the pyrope from those deposits. Considering inclusions in rock crystal artifacts from the Poznan collection it was assumed that the mineral was also of the Bohemian origin.