Določanje vrste in provenience granatov iz S-fibul s poznoantičnega najdišča Lajh-Kranj

Kos, Saša (author), Kramar, Sabina (mentor), Dolenec, Matej (comentor)

Izdelava ornamentiranega kovinskega nakita, na katerem se kot okrasni kamni pojavljajo rdeči granati, je značilno za obdobje velikih preseljevanj narodov od 4. do 8. st. n. št.. Do danes so z določanjem kemijske sestave okrasnih kamnov in trdnih vključkov ugotovili uporabo petih tipov granatov in njihov možni geološki-geografski izvor – dveh tipov almandina, skupino granatov srednje sestave pirop-almandina in dveh tipov piropa. Almandini in pirop-almandini naj bi izvirali iz Indije in Šri Lanke, piropi pa iz bodisi Češke Portugalske in/ali Vzhodne Afrike. V poznoantičnem grobišču Lajh v Kranju so našli večje število brošk z rdečimi granati.. V našem delu smo analizirali 19 granatov s šestih S-fibul z arheološkega najdišča Lajh v Kranju z namenom strukturno-kemične karakterizacije in določanja provenience. Strukturno-kemično sestavo S-fibul smo določili z uporabo nedestruktivnih analitskih metod – ramanske mikrospektroskopije, rentgenske fluorescenčne spektroskopije in vrstične elektronske mikroskopije z emisijsko disperzijskim spektrometrom. Z optično mikroskopijo smo identificirali tudi trdne vključke, nekatere smo identificirali tudi z ramansko mikrospektroskopijo. Kemijsko sestavo granatov s fibul smo primerjali z granati iz različnih svetovnih nahajališč in literaturnimi podatki. Sestavo kovinskih elementov fibul smo določili z metodo XRF. Izsledki preiskav so pokazali, da so fibule izdelane iz treh različnih zlitin: iz dveh različnih pozlatenih zlitih srebra in bakra s primesmi svinca, cinka in kositra ter iz brona z dodatkom svinca; na njih pa prevladujejo železovi različki granatov piralspitne serije - almandini, s primesmi kalcija in magnezija, in ustrezajo tipu I almandinov. Na dveh fibulah so prisotni tudi almandini z nekoliko višjo vsebnostjo kalcija, magnezija in mangana, ki ustrezajo tipu II almandinov. V granatih so prisotni vključki apatita, cirkona, kremena in sljud, v almandinu tipa II so prisotni tudi vključki minerala sillimanita, ki kaže na nastanek granatov v srednje do visoko metamorfoziranih kamninah. Na podagi rezultatov preiskav in dostopnih literaturnih podatkov smo zaključili, da granati najverjetnje izvirajo iz Indije.

• Language: Slovenian
• Keywords: granati, provenienca, vključki, S-fibule, Lajh, pozna antika
• Work type: Master's thesis/paper
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Year: 2019
• PID: 20.500.12556/RUL-109983
• Publication date in RUL: 11.09.2019

Secondary language

• Language: English
• Title: Determination of type and provenance of garnets from S-fibulae from the Late Antique site Lajh-Kranj

Abstract

The production of ornamented metal jewelry, which is decorated with red garnets, is typical for the Great migrations period from 4th to 8th century AD. By determining the chemical composition and mineral inclusions of gemstones, five different types of garnets and their probable geological-geographical origin was identified to date – two types of almandine, garnets with the intermediate composition of pyrope-almandine and two types of pyrope garnets. Almandine and pyrope-almandine garnets are supposed to originate from India and Sri Lanka, with pyropes originating from either Czech Republic, Portugal and/or East Africa. In the Late Antique Lajh cemetery in Kranj, a large number of brooches (fibulae) with red garnets were found. We analysed 19 garnets from six S-fibulae from Lajh archaeological site in Kranj with purpose of structural-chemical characterisation and provenance determination. We determined the structural-chemical composition of garnets using non-destructive analytical methods – Raman microspectroscopy, X-ray fluorescence spectroscopy and scanning electron microscopy coupled with emission dispersive spectrometer. Solid inclusions were identified with optical microscopy and some with Raman microspectroscopy. The chemical composition of garnets from fibulae was compared to garnets from various deposits around the world and literature data. The metal was qualitatively defined using results of XRF spectroscopy. The results show that fibulae are made of three different alloys: two types of gilded silver-copper alloy with addition of lead, zinc and tin, or with bronze with the addition of lead. Garnets from fibulae are mainly iron varieties of garnets of piralspite series – almandines with low calcium, magnesium and manganese contents, which correspond with type I almandines. On two fibulae are also present almandines with high calcium, magnesium and manganese content, which correspond with type II almandines. Inclusions of apatite, zircon, quartz and mica are present in garnets, and inclusions of sillimanite are present in type II almandine, indicating the formation of garnets in medium to highly metamorphosed rocks. Based on of our analyses and available literature data, we conclude the purposed origin of these garnets is India.

• Keywords: garnets, provenance, inclusions, S-fibulae, Lajh, the Late Antique