XRD, SEM/EDX and micro-Raman spectroscopy for mineralogical and chemical characterization of iron slags from the Roman archaeological site of Forua (Biscay, North Spain) Haizea Portillo a, ⁎, Maria Cruz Zuluaga a , Luis Angel Ortega a , Ainhoa Alonso-Olazabal a , Xabier Murelaga b , Ana Martinez-Salcedo c a University of the Basque Country, Dept. of Mineralogy and Petrology, P.O. Box 644, E-48080 Bilbao, Spain b University of the Basque Country, Dept. of Stratigraphy and Palaeontology, P.O. Box 644, E-48080 Bilbao, Spain c ARKEON, Plaza Julio Lazurtegui, 6 4° dcha., 48014 Bilbao, Spain abstract article info Article history: Received 17 August 2017 Received in revised form 28 November 2017 Accepted 12 January 2018 Available online 16 January 2018 The Roman village of Forua (North Spain) was an important iron production and distribution centre during the 1st-4th centuries AD. Different metallurgical materials at the archaeological site were identified as forged slag, bog ore mineral and refractory materials used in the walls and on the floor of furnaces. The samples were studied by macroanalysis and microanalysis techniques. The mineralogical characterization was carried out via optical microscopy and X-ray powder diffraction, and the textural characteristics and the composition of individual phases were determined using scanning electron microscopy coupled with electron-dispersive spectroscopy, and by Raman microspectroscopy. Mineral associations not only reflect furnace cooling rates and temperatures but also indicate quartz was the main flux used. The microanalysis results reflect the elements that constituted the slags and other materials from the forge and the worked metallic materials. The results showed the slags orig- inated from iron smithing, which also was confirmed by the presence of iron particles. The ore materials consisted of goethite. © 2018 Elsevier B.V. All rights reserved. Keywords: XRD SEM/EDX Micro-Raman spectroscopy Smithing slags Roman period North Spain 1. Introduction In the past, iron objects were produced in a process consisting of two or sometimes three steps. Iron ore, usually iron oxides, was roasted in order to lose volatiles, such as hydrogen and sulphur. Then the ore was reduced in solid state by heating in a closed furnace with charcoal. This is known as direct or bloomery smelting [1, 2]. The ore changed into a metallic state by the carbon monoxide produced in the furnace, resulting in a porous mass of iron and impurities called “bloom”. As a re- sult of the smelting process between 10 and 20% of ore mass changed into the iron bloom while the rest was transferred into the iron slag [3]. The solid iron bloom incorporates such other substances as silica, alumina and unreduced iron oxides, resulting in iron smelting slags, and charcoal. In the next step the bloom was refined during the smithing process to remove adhered slags until it was shaped into a finished product. The smithing process was performed in two stages and consisted of heat- treating in a hearth and hammering on an anvil. In the primary smithing process, adhered slag inclusions and charcoal were removed from the bloom, thus consolidating the metal into a more compact and manageable bar. Then, in the secondary smithing process the iron was shaped into the final object [1, 4–7]. Wastes associated with both stages form the smithing slags, which are accumulations of fused residual materials at the bottom of the hearth. Thus, two main slag types are generally formed, the smelting slag, correspond- ing to the gangue material discarded from the ore, and smithing slag, formed by an accumulation of fused materials at the hearth [2]. Both smithing and smelting processes result in the production of numer- ous types of silicate slag. Smithing and smelting slags are from differ- ent pyrometallurgical stages and often are hardly distinguishable chemically and mineralogically [6]. However, the archaeological context is able to determine the type of slags due to the elements of installation found in the excavations (e.g., type of furnaces, extant equipment). Slags can also be differentiated by the type of morpho- logical characteristics, chemical composition and phase composition and microstructure [1, 2, 6, 8]. Thus, within the by-products of the metallurgical process, slags are often the only relicts of ancient pyro- metallurgy and represent a valuable source of information regarding ancient metallurgical technology and economy [7]. Microchemical Journal 138 (2018) 246–254 ⁎ Corresponding author. E-mail address: haizea.portillo@ehu.eus (H. Portillo). https://doi.org/10.1016/j.microc.2018.01.020 0026-265X/© 2018 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Microchemical Journal journal homepage: www.elsevier.com/locate/microc