Ceramic clays are among the most complicated of ceramic systems because of the very intricate relationship between the behavior of minerals during ceramic processing and their modifications during heating. A major challenge is to predict the phase changes in clay ceramics. The aims of this study were to establish reference data of ceramic products that can be formed based on the mineralogical compositions of the local raw materials. These data, in turn, can be compared with archeological ceramics in order to study their origins.

The mineralogical compositions and modifications during firing (550–1100°C under oxidizing conditions) of seven clayey materials sampled from the main clay deposits of northern Morocco were evaluated by X-ray powder diffraction. Two groups of clays were distinguished according to the type of neoformed high-temperature minerals: non-calcareous clays and calcareous clays. For the non-calcareous raw materials, spinel was produced at 950°C. Cristobalite and mullite were formed at temperatures in excess of 1000°C from clays that contain illite, kaolinite, and chlorite. In clays containing vermiculite and large amounts of chlorite, hematite was formed at temperatures in excess of 950°C. Firing of calcareous clays at temperatures >950°C yielded Ca-silicates (diopside, gehlenite and wollastonite), spinel, cristobalite, hematite, and feldspars. Mullite may also form in the calcareous clay products when the carbonate content exceeds 10%.

A kaolin deposit from Mankon (northwest Cameroon) was prospected and studied for potential applications in ceramics. Six samples were investigated with X-ray diffraction (XRD), infrared (IR) spectroscopy and scanning electron microscopy (SEM) to determine the mineralogical composition and with X-ray fluorescence (XRF) to determine the chemical composition and properties for ceramic applications. The main minerals in the clays are kaolinite/halloysite and anatase associated with alunite, illite, gibbsite and maghemite. The kaolin samples have abundant organic matter (4–10%) and low absorption of methylene blue (0.2–2.5 meq/100 g), while SiO2 (33.28–56.31%) and Al2O3 (19.26–35.87%) are major oxides. The particle-size distribution derived from sieving and the hydrometer method indicates that 12–38% of the samples are in the <2 μm clay fraction. The clays have low to moderate plasticity (7–21%). One sample with K-feldspar and plagioclase displays the necessary properties for red ceramic products. SEM confirmed the occurence of halloysite in sample M9. The high kaolinite/halloysite content (64–97%), associated with low Fe2O3 content (0.5–1.4%) demonstrates that five samples are suitable raw materials for white firing industrial kaolin.

Three clayey materials named MY3, KK and KG originating from the Foumban region (west Cameroon) were analysed to determine their granulometry, plasticity, major-element chemistry and mineralogy. Dilatometric and ceramic behaviour were also investigated. Clays were shaped by uniaxial pressing in a steel mould. Shaped samples were heated at 1300, 1400 and 1500°C. The end products were characterized in terms of their density, porosity and compressive strength. Raw materials differ in terms of their mineralogical composition, grain-size distribution, Al2O3 content and the nature and abundance of impurities inducing specific thermal behaviour during dilatometric analysis and sintering tests. The final material properties may be related to the main features of the raw materials used.

Five clay deposits in Foumban, west Cameroon, were studied for their morphological, mineralogical and geochemical properties to determine their suitability for ceramics. The clays were examined with X-ray diffraction, X-ray fluorescence, thermal gravimetric analysis and Fourier-transform infrared spectroscopy. Field studies showed that a homogeneous clayey layer occurs at the upper part of the laterite cover of the interfluves, while the valleys are occupied by a clayey heterogeneous hydromorphic material. The clays are composed of kaolinite, illite, smectite and chlorite, associated with quartz, K-feldspars, plagioclase, goethite, traces of rutile and hematite. Geochemical analyses of these samples show a relatively large amount of SiO2 (45–71%), Al2O3 (14–31%) and relatively little Fe2O3 (up to 11%), suggesting weathering of mainly granitic and rhyolitic parent rocks. The majority of these clays may be used in the production of structural ceramics such as bricks (refractory or not) and tiles. The relatively high proportion of the alkalis (K2O + Na2O; 6–8%) in some samples from Marom and Njindare areas might be responsible for the low firing temperatures. The abundance of smectite limits the application of some Koutaba and Marom clays for structural ceramics, while the high Fe2O3 contents (>8%) in some Bangourain clays indicate that some pre-treatment might be necessary prior to use.

The physicochemical and mineralogical characterization of the <250 μm particle-size fraction from six clay-rich samples from the Sabga deposit (north-west, Cameroon) were carried out to evaluate their potential applications. The major clay mineral is dioctahedral smectite and minor kaolinite is present in three of the clay samples. Cristobalite, feldspars, ilmenite and heulandite are accessory minerals. Application of the Greene-Kelly test revealed that the smectite present is montmorillonite. The chemical composition (wt.%) of the bulk clays consists of (66–70%) SiO2, (13–16%) Al2O3 and (2–7%) Fe2O3. Physico-chemical characterization of the clays showed that the cation exchange capacity (CEC) and the specific surface area range from 38 to 46 meq/100 g and from 33 to 90 m2/g respectively. The physical and chemical properties are fully compatible with potential uses in environmental applications. After purification and chemical modification, these materials could also be used in refining edible oil as adsorbent, waste water treatment and wine technology.

In the western High Atlas basin, the evolution of the clay assemblage of the Upper Jurassic–Cretaceous sedimentary series is controlled by palaeogeographic changes of the basin and by burial diagenesis.The effects of burial are expressed by an increase in the proportions of illite and chlorite with depth, a decrease of expandability of smectite minerals and by a decrease in the Kübler Index.Kaolinite is preserved at greater depths than smectite, but also tends to diminish in abundance. TEM observations show that idiomorphic pseudo-hexagonal crystals of illite increase in size and abundance downwards, especially in the sandy levels.In the Agadir section, the main change in the clay mineral evolution related to late diagenesis occurs at the Mid-Albian, corresponding to a burial depth of about 1800 m; in the Essaouira section it occurs at the Lower Tithonian at a burial depth of about 2100 m.Considering the different geothermal gradient between Agadir (36ºC km–1) and Essaouira (27ºC km–1), the disappearance of smectite occurs at the same temperature in these two sites (60 to 65ºC).

Clayey deposits of Nanga-Eboko (central Cameroon) were studied to assess their potential as building materials. Characterization was performed using XRD, FTIR, XRF, DTA/DTG and firing testing. Clays appear as discontinuous pockets with the same textural characteristics in three villages located on both sides of the Sanaga River. The average thickness of the exploitable layer is about 3m. The estimated tonnage ∼7–17×105 m3 can supply a brick industry of great importance. SiO2 (∼70%), Al2O3 (∼15%) and Fe2O3 (∼4%) are the predominant oxides of the natural clays. Quartz (∼55%), kaolinite (∼33%), illite (∼5%) and K-feldspar (∼4%) are major minerals. Clays are not suitable for building construction due to their fine-grained size and high plasticity properties. Firing properties of bricks (950 and 1050°C) are good despite the high shrinkage values. Therefore the addition of “degreasers” is recommended to control shaping and drying.

The clay mineralogy of Pleistocene sediments of eleven sediment cores at three ODP sites from 30°N to 60°N northwestern Atlantic Ocean has been investigated. The sediments are characterized by the presence of random illite-vermiculite mixed layers (I-V) (up to 32% of the clay mineral assemblage). The I-V clays are much more abundant during interglacial periods than during glacial ones. They are attributed to detrital supply through erosion of high-latitude continental areas from which they are derived mainly from chemical weathering of micaceous phyllosilicates. Their spatial distribution and the specific conditions for their formation through weathering suggest that I-V mixed layers are mainly derived from the Canadian Shield. They were transported from their source to marine deposition areas by rivers, deep water masses or nepheloid layers. Due to the specific conditions required for the formation of I-V, its occurrence and abundance are used as a palaeoclimate and palaeocirculation proxy for northwestern Atlantic Pleistocene sediment.

This study focuses on the mineralogical and geotechnical characterization of northern Moroccan clays from the Tangier and Tetouan areas and compares them with the main clay deposits used in the Moroccan ceramic industry (from Meknes, Fes, Salé and Safi regions). Sampled clays were analysed by X-ray diffraction on bulk and clay (<2 μm) fractions to identify the mineralogical assemblages of the clay outcrops. Further analyses were conducted to determine the particle size distribution (laser diffraction particle analyser), the total organic matter content (Loss- On-Ignition measurements) and the Atterberg limits of the raw clays. The study aims at investigating the spatial variability of the clay samples and at evaluating their potential application as raw materials in the ceramic industry.

Tetouan and Tangier clays are characterized by diversified mineralogical assemblages (in particular a variable proportion of clay, quartz and calcite) compared with the Meknes, Fes, Salé and Safi clays (high clay content, quartz and calcite). The clay fraction of the Tetouan and Tangier samples is dominated by illite and kaolinite with variable amounts of chlorite, smectite and/or vermiculite. Illite is the dominant phase in the Meknes, Fes, Safi and Salé clays, but is associated with kaolinite. No direct relationship between the mineral assemblage composition and the lithology of the series was found.

The clays materials studied consist generally of fine particles with medium to high plasticity and low organic matter content. Due to their mineralogy, grain-size distribution and plasticity the clays appear to be suitable as raw material for the growing Morocco ceramic industry.

The Maastrichtian-Palaeogene series of the Western High Atlas and Meseta Basins in Morocco are particularly rich in palygorskite. The present work is aimed at clarifying the genesis of palygorskite from the interbedded facies and gaining an understanding of their relationships with the depositional environment. The mineralogical characteristics of palygorskite from these series were studied by X-ray diffraction (XRD) and electron microscopy (SEM/TEM). The palygorskite content and microstructure show large geographical and stratigraphical variations in the deposits studied. The palygorskite occurrence is directly related to palaeobathymetry, since it is the dominant clay mineral in shallow marine and restricted environments. According to the morphology of palygorskite crystallites, four types of textures were distinguished. These types of palygorskite are polygenetic, formed by chemical precipitation, by the recrystallization of smectite clays or reworked by wind or water from sub-aerial environments. The difference between the two studied sub-basins with respect to palygorskite occurrence is attributed to the palaeomorphology of the hinterlands, to the tectonic differentiation and to the physical-chemical conditions of seawater.

Smectitic clays from the Sabga and Bana areas, western Cameroon were treated with sulfuric-acid solutions of various concentrations – 0.5, 0.7, 1.0 and 4.0 N – at 80°C for 2 h. The mineralogical, physicochemical and morphological characteristics of the samples treated were analysed using several techniques. The sulfuric acid caused structural modification of the dioctahedral smectite. The accessory minerals such as cristobalite, quartz, feldspars and anatase remained unaltered by the acid attack. The supernatant solutions after acid treatment contain Mg, Ca, K, Na, Si, Al and Fe as a result of partial dissolution of octahedral and tetrahedral cations. The activated clay samples exhibited a smaller cation exchange capacity (CEC) and the specific surface area (SSA) increased with increasing concentration of sulfuric acid, ranging from 65 to 134 m2/g for the sample from Bana and from 74 to 84 m2/g for the sample from Sabga. The different SSAvalues were affected by the relative abundance of smectite and cristobalite (SiO2/Al2O3 = 2.2 and 6.5, respectively, from Bana and Sabga). The activated clays from Bana and Sabga displayed interesting physicochemical and textural properties and can be considered as promising adsorbents for the bleaching of vegetable oils.

Thirty clay samples collected from three hills in Koutaba (west Cameroon) were characterized in order to evaluate their potential use as raw materials for ceramics. After preliminary mineralogical identification by X-ray diffraction, three representative samples from the three different hills, referred to hereafter as K1M, K2M and K3M, were selected for further investigation by X-ray fluorescence, plasticity, granularity and thermogravimetric analysis. The main clay minerals are kaolinite (32–51%) and illite (up to 12%). Additional major phases are quartz (32–52%), goethite (6–7%) and feldspars (0–4%). The chemical composition showed variable amounts of SiO2 (60–72%), Al2O3 (15–20%) and Fe2O3 (1–9%), in accordance with the quartz abundance in all of the samples studied. The particle-size distribution showed a large proportion of silty fraction (64–88%) with moderate sandy (9–19%) and clayey fractions ( < 5% for K2M, 12% for K1M and 20% for K3M). All of the clays showed moderate plasticity-index values (8–11%). Because of these characteristics, K1M and K3M may be suitable for use in common bricks and hollow ceramic products. Sieving or the addition of ball clays is recommended to increase the plasticity of sample K2M for use in common bricks.