Comment la composition chimique peut influencer la couleur des roches magmatiques et sédimentaires: Cas des roches du Haut Atlas de Maroc

peer reviewedIn spite of color being one of the physicochemical parameters most commonly used to characterize a rock, very limited studies have studied the correlation between the nature, chemical composition, and color of a rock. This study presents a new approach for quantitatively assessing the relationship between these three parameters for specific rocks (example of igneous and sedimentary rocks) collected from the High Atlas of Morocco. A spectrophotometer was used to measure the color of samples, and the measurements were expressed in CIE L*a*b* color system units then converted to Hex color codes. Whereas, the chemical composition of samples was carried out by X-ray fluorescence. The most abundant oxides in magmatic rock samples are SiO2, Al2O3, Fe2O3, MgO, and CaO, while K2O, Na2O, TiO2, and P2O5 are generally found in trace concentrations. Two categories of clays were studied, non-calcareous raw materials without carbonate contents ( 10%). Phosphate samples are rich in phosphorus (4.4%-17.5%) and CaO (11.2%-42.7%) with relatively low contents of SiO2 (28.5%-52.2%), Al2O3 (3.1%-17.5%), and Fe2O3 (1.1%-6.6%). Results show that the change in the content of these elements from one rock type to another may be indicative of rocks with particular characteristics that do have an impact on color. The main coloration agent of clays was iron, Fe2+, and Fe3+ ions can color clay minerals either red or green or in various shades of orange and brown. However, in marls and phosphates, the high concentration of carbonates inhibits this iron effect by affecting a* (red) and b* (yellow) color parameters, which leads to grayish materials. The same applies to magmatic rocks rich in Fe2O3 and CaO

Characterization of the historical monuments ceramics of Marrakech region and prospection of restoration materials

Archaeological ceramics from El Badi Palace, Saadian Tombs and Aghmat historical sites located in the region of Marrakech were analyzed by a multi-analytical approach based on Xray diffraction, fluorescence and microscopic analyzes to study their physical, chemical and textural characteristics. Clay samples were also collected from different quarries in the Marrakesh and Fez region, and then analyzed using the same techniques. The aim is to determine the manufacturing technology, properties and origin of the raw materials used by the Almoravide and Saadian dynasties in construction. Experimental cooking tests on ceramic bodies were also carried out in order to determine the firing temperatures used in traditional ovens during these times. According to the results obtained, the Saadians used carbonated clay to make the zellige, one of the key elements of decorative ceramics; the raw material used comes from the region of Fez. The estimated firing temperature for these materials is between 700 and 800 °C for the El Badi palace and between 800 and 900 °C for the Saadian tombs in an oxidizing atmosphere. The glaze is mainly composed of lead and silica, the coloring agents are conventional, iron (Fe3+) for the yellow glaze, manganese (Mn3+) for the black glaze, copper (Cu2+) and phosphorus (P) for the blue glaze. The texture of the glaze/shard interface was studied using optical microscope and cathodoluminescence; results show that the glaze was applied directly to the ceramic support without slip or intermediate layer. The utility ceramics (irrigation channels) and structural ceramics (red bricks) were made from a local clay rich in iron from the Marrakech region, the firing temperature was around 700 °C for the channels and 900 °C for bricks. The archaeological ceramics collected at the Aghmat site are composed of fragments of tiles, bricks, irrigation channels and pottery. The structural ceramic was made from a local non-carbonated clay rich in iron, fired at a temperature above 900 °C, on the other hand the utility ceramics come from a carbonated raw material collected in the surroundings of the village of Aghmat , the estimated cooking temperature for these materials is between 700 °C and 900 °C. In order to improve the quality of the materials used in the restoration of the studied monuments, we have also made experimental briquettes by varying composition of raw materials and the cooking parameters. The results obtained show that the Benjlikh site clays in Fez are the most suitable for the restoration of these buildings; the appropriate cooking temperature is around 850 °C to 950 °C, with a slow firing cycle and a bearing of at least 4 hours. These parameters provide good quality materials which combine strength, durability and cutting ability.Bilateral Cooperation Project Wallonie Bruxelles-Maro

Saadien Mosaic (Zellige) from historical monuments of Marrakech, Morocco: Degradation state and production technology

This study is focused on Saadian ceramics called zellige from the archaeological sites of "El Badi palace" and "Saadian Tombs" (Marrakech, Morocco) dated in late 16th Century and classified as world heritage by UNESCO in 2008. A multi-analytical approach based on optical microscopy, cathodoluminescence, scanning electron microscopy, X-ray fluorescence and X-ray diffraction investigations and re-firing tests on ceramic supports has been used,in order to determineraw materials source, technical manufacturing and firing temperatures used by the Saadian artisans. Production technology, microstructure and the chemical compositionsuggest that the zellige pieces used in the construction of Saadian monuments in Marrakech are either imported from Fez, i.e. the main center of production of the zellige in Morocco, or manufactured locally in Marrakech according to the current standards and procedures in Fez. The calcareous clay raw materialwas used to manufacture these ceramics, but firing temperature was different. Zellige of El Badi palace was fired at a maximum temperature of 700°C in oxidizing atmosphere, while the one of Saadian Tombs was fired in the range 900-950 °C. The low firing temperature for Zellige facilitates the pieces cutting but it is responsible for the poor quality of these materials due to the absence of the vitreous phases. The results provide a scientific support for decision making in future conservation and restoration strategies of historical monumentsacross Morocco.Etude de la dégradation des céramiques des monuments historiques de la région Marrakech (Maroc) et prospection des matériaux de substitutio

Analytical study of ancient ceramics from the archaeological site of Aghmat, southern Morocco

peer reviewedThis paper explores Aghmat archaeological materials (VII centuries) using two types of ceramics, come from a recent archaeological excavation in Aghmat (Morocco) in order to enhance documentation, conservation and restoration issues, then putting into value the architectural heritage. Fortuitously discovered in 2005, Aghmat village has allowed the reformulation of several hypotheses about Aghmat population skills in construction and handicrafts. Even though the areal extent of this archaeological site exceeds 20 Km2, no traces of furnaces have been found yet, only ruins of buildings and streets. Bricks and pottery samples were the most abundant types of ceramics founded. Mineralogical and chemical analyses of this materials provided information about the origin of raw materials and manufacturing process. The chemical compositions indicated that SiO2, Al2O3 and Fe2O3 are major elements while K2O and MgO are less abundant. The ceramics were produced using at least two raw materials, non calcareous clay of permo-triassic age for bricks, and carbonate quaternary clays for pottery samples, as the calcium oxide content is generally more than 10%

Caractérisation des argiles de Fès (Nord Maroc) pour une potentielle utilisation dans l'industrie céramique

peer reviewedClays from the Saïss basin (northern Morocco) used traditionally in the ceramic industry in the Fez area were studied using mineralogical and physicochemical techniques to evaluate their potential suitability as raw materials for ceramics manufacture. X-ray diffraction was used to determine their mineralogical composition. The physical properties determined were particle-size distribution and consistency limits. The chemical composition was determined using X-ray fluorescence analysis and Fourier-transform infrared spectrometry. The structural changes of the mineral phases in the raw materials during firing were studied over a temperature range of 500–1000°C. In the pottery site from Fez, generally potters use a mixture of 25% fine clay (ARFS) from the upper part of the Miocene marls and 75% sandy clay (ARFR) from the lower part of the Miocene marls. The ARFS clay yielded very rigid specimens after firing that artisan potters would find difficult to handle so as to produce desired shapes and sizes. However, the specimens obtained from ARFR clay show signs of faltering. The mixture of these two clayey materials from this pottery site is therefore necessary to obtain the optimal paste for ceramic proposes. The chemical compositions indicated that SiO2, Al2O3, CaO and Fe2O3 are major minerals, with trace amounts of K2O and MgO. Quartz, feldspars and clay minerals prevail in all samples. Kaolinite, illite and smectite are the dominant clay mineral phases, with traces of chlorite and interstratified illite–smectite. The classification of these samples using appropriate ternary diagrams showed that the proportions used in the mixture produce a new material with adequate characteristics for the production of traditional ceramics.9. Industry, innovation and infrastructur

Moroccan clay deposits: Physico-chemical properties in view of provenance studies on ancient ceramics

Features of clayey raw materials from most important traditional pottery centers in the vicinity of the main medieval sites in Morocco, and their fired products were investigated. Besides clay from the North of Morocco, the used raw material was illitic clays (10–100%) and smectite-rich clays (0–67%) with variable amount of kaolinite, quartz and feldspars. Chlorite was also present in a small amount. The main major oxides were Si2O, Al2O3 and CaO. The fired tests (800–1100 °C) displayed a decrease in open porosity of the sintered clay by raising the temperature, mainly from 1000 °C due to the inception of melting. This change was coupled with the change in mineralogical composition. New crystalline phases as Ca silicates (diopside and gehlenite), hematite, spinel and mullite occurred during firing process, attesting to the inception of melting and were responsible for porosity reduction. Reference clays for pottery were established based on the clay mineralogy and chemical composition. The present study would help to answer some archeological questions concerning possible sourcing areas for archeological ceramics, to determine techniques for the production of artefacts, and then to interpret cultural influences. Furthermore, the obtained results will support the inception of development of a compositional database for Moroccan pottery

Non-destructive portable X-ray Fluorescence (pXRF) method for the characterization of Islamic architectural ceramic: Example of Saadian tombs and El Badi palace ceramics (Marrakech, Morocco)

Archeological decorated ceramics from the Saadian tombs and El Badi palace sites (Marrakech, Morocco) have reached an advanced deterioration phase; the glazes have been increasingly weakened due to human and environmental impacts over time. Portable X-ray Fluorescence (pXRF) was performed in situ and on samples selected from these two monuments, in order to define the chemical agents responsible for the color of the studied glazed ceramics and to determine their evolution over time to help find answers and link between degradations and chemical compositions of different type of glazes. The results show that all samples are lead-silica type glazes with 25–59 wt% of PbO and 51 wt% of SiO2. The coloring agents used for the original glaze are conventional, copper (Cu2+) for the green color, iron (Fe3+) and manganese (Mn2+) for the yellow and black glaze. Phosphorus (P2O5), comes from carbonate mineral phases, is responsible for the blue opalescence of glazes. The study reveals that the ceramic industry has evolved recently in Morocco; elements such as calcium and potassium are currently used in small quantities while lead is increasingly used as flux in the glaze mixture. Iron and copper are still used for black, yellow and green colors, while the use of phosphorus has been replaced by other elements such as cobalt and copper.Bilateral Cooperation Project Wallonie Bruxelles-Maro

Mineralogical and Geochemical Characterization of Archaeological Ceramics from El Badi Palace (XVIth Century), Morocco

Textural, mineralogical and chemical characterization of archaeological ceramics (zellige) of the El Badi Palace (Marrakech, Morocco), the main islamic monument from the Saadian period (XVIth century), has been performed, to enhance restoration issues and to determine technology of manufacturing. A multi-analytical approach based on optical and Scanning Electron Microscopy (SEM), cathodoluminescence, X-ray fluorescence (XRF) and X-ray diffraction (XRD) was used. Re-firing tests on ceramic supports were also performed to determine the firing temperatures used by the Saadian artisans. A calcareous clay raw material was used to manufacture these decorative ceramics. The sherds were fired at a maximum temperature of 800°C in oxidizing atmosphere. The low firing temperature for zellige facilitates cutting of the pieces but also causes fragility to these materials due to the absence of vitreous phases

Mineralogical and physicochemical characterization of the Jbel Rhassoul clay deposit (Moulouya Plain, Morocco)

This study aims at the mineralogical and physicochemical characterization of clays of the Missour region (Boulemane Province, Morocco). For this, three samples were collected in the Ghassoul deposit. The analyses were carried by X-ray diffraction (XRD), X-ray fluorescence (XRF) and Scanning Electron Microscopy (SEM). The thermal analysis from 500 to1100°C was also performed on studied samples, and the fired samples were characterized by XRD and SEM. The XRD results revealed that raw Ghassoul clay consists mainly of Mg-rich trioctahedral smectite, stevensite-type clay, which represents from 89% to 95% of the clay fraction, with a small amount of illite and kaolinite. The associated minerals are variable amount of quartz, dolomite, hematite, gypsum and K-feldspars. The chemical analysis confirms the presence of Mgrich smectite (stevensite) with largest amount in sample containing the highest MgO. The SEM micrographs revealed the presence of automorphous structures with petalslike shape typical of smectite. The Thermal transformations determined by X-ray diffraction indicated that stevensite was transformed to enstatite from 800ºC. Diopside starts to appear from 700°C, which is confirmed by SEM observations, and the quartz is transformed to cristobalite when the temperature exceeds 1100°C