Interdisciplinary (mineralogical-geological-archaeological) study on the tegular material belonging to the legion XIII Gemina from Alburnus Maior (Roșia Montanã) and Apulum (Alba Iulia): possible raw materials sources

Cercetări Arheologice 13, 2006, 413-436
https://doi.org/10.46535/ca.13.22



Interdisciplinary (mineralogical-geological-archaeological) study on the tegular material belonging to the legion XIII Gemina from Alburnus Maior (Roșia Montanã) and Apulum (Alba Iulia): possible raw materials sources


Authors: Corina Ionescu, Lucreția Ghergari, Ovidiu Țentea

Keywords: brick stamps; samples; mineralogical and petrographical analysis

Abstract:

From a high number of bricks and tiles found at Alburnus Maior (Roşia Montană) and Apulum (Alba Iulia) (Romania), twenty two fragments were studied. The ceramics consists mainly of a matrix with crystalline and/or amorphous fabric, showing different degrees of sinterization and vitrification. In the matrix variable amounts of magmatic, metamorphic and sedimentary lithoclasts, various crystalloclasts (quartz, feldspar, mica), and rare ceramoclasts and bioclasts are present. Regarding the grain size, the ceramics is mainly lutitic-siltic-arenitic, with a contribution of arenaceous-sized grains exceeding 15% and reflecting the coarse category for all samples. The composition of the lithoclasts and crystalloclasts indicates that quartz sands were used as temper materials for the ceramics. Quartzite, granite-granodiorite, basalt, andesite/basaltic andesite, gneiss and limestone are ubiquitous lithoclasts. Microscopical observations on the matrix as well as the X-ray diffraction indicate the use of polymictic clays, consisting mainly of illite, kaolinite ± smectite ± calcite ± micas as raw materials. The clays seem to be similar for both, the Roşia Montană and the Alba Iulia artefacts. The firing temperatures were inferred from both, the thermal changes of primary minerals such as the fissuring of quartz, the decomposition of calcite, the contraction holes around some lithoclasts, the change of the anisotropy of clay minerals, and the forming of melt-glass, gehlenite, wollastonite and hematite, and the disappearance of some lines of clay minerals, the presence of hematite, gehlenite and wollastonite lines, the modification of calcite lines in X-Ray diffractograms. Based on the firing temperatures, the ceramic artefacts were classified in three categories: – Type I ceramics, fired at lowest temperature (800-850o C); – Type II ceramics, fired at 850-900o C; – Type III ceramics, fired at 900-950o C. In the Alba Iulia site well-fired ceramics are prevalent (850-950o C), while the Roşia Montană ceramics are mainly fired at lower temperatures (800-900o C). Being based on the mineral composition of the matrix (illite, kaolinite ± smectite ± calcite + mica), we presume that clays with an according composition, outcropping west of Sântimbru, east of Şard and west of Alba Iulia were used as raw materials. The mineralogical and petrographical composition of the crystalloclasts and lithoclasts respectively, in the ceramics both from Roşia Montană and Alba Iulia is similar. Granites and granodiorites are similar to those crossed by the Arieş river, north of Alba Iulia, basalts, basaltic andesites, radiolarites are surely originated from the Mesozoic ophiolitic zone outcropping westwards of Alba Iulia and limestones outcrop westwards of Alba Iulia, together with the ophiolites.These lithoclasts are also found in the alluvial sediments of the Mureş river downstream the confluence with the Ampoiu river. Thus, we presume that the temper was most likely mined from the right bank of the Mureş river, south-east of Alba Iulia. Even today this location provides quartz sands, used for bricks and tiles manufacture.

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How to cite: Corina Ionescu, Lucreția Ghergari, Ovidiu Țentea, Interdisciplinary (mineralogical-geological-archaeological) study on the tegular material belonging to the legion XIII Gemina from Alburnus Maior (Roșia Montanã) and Apulum (Alba Iulia): possible raw materials sources, Cercetări Arheologice, Vol. 13, pag. 413-436, 2006, doi: https://doi.org/10.46535/ca.13.22


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