To a mineralogist, minerals are defined primarily by their crystal structure and chemical composition. Many minerals of industrial importance retain this identity in their final application. For the producer and end user, the physical properties of these industrial mineral products such as size and shape distribution, refractive index, density, hardness, refractoriness and colour are of primary importance, since it is the combination of these, together with its surface chemistry, which gives the mineral its functionality. As a result, minerals which are very different in structure and origin but have many similar physical properties, such as kaolin and calcium carbonate, are often used in very similar roles and in similar applications.

Examples of mineral use in diverse applications such as paper, paints and coatings, polymers and films show how the physical properties of different minerals are exploited and engineered to provide optical, mechanical and rheological performance and to minimise cost. Industrial mineral producers have been manipulating these properties for many decades and continue to do so in search of improved performance and new applications. As new high performance materials become more commonplace, the challenge is to find new ways of transforming minerals to provide the necessary functionality for them.

It has been established that disagreements between different methods of particle size determination of clay minerals can be ascribed to the non-spherical shape of the clay particles. However, by having aspect ratios available, particle sizes can be harmonized. One frequently used approach to obtain aspect ratios is to compare particle sizes originating from at least two devices operating on the basis of different physical principles. In this contribution aspect ratios of nine kaolinite-dominated and one dickite-dominated sample were determined by conductometric titrations. The aspect ratios obtained were then successfully used to correlate particle size distributions from dynamic laser scattering and acoustic spectroscopy.

The unique properties of clays make them suitable for a large number of applications. Among the procedures that can be used to characterize clayey materials, the assessment of the abrasion and the abrasiveness index can be employed to predict the mechanical behaviour of clay samples. However, only a limited number of references to these testing procedures are available in the literature. Several Portuguese clayey samples were collected and the <63 μm fraction was analysed. The main clay minerals present are kaolinite, illite and smectite. The abrasiveness index depends on the granulometric and mineralogical compositions. A lower abrasiveness is induced by the presence of a high abundance of the <2 μm fraction, small mean particle size and a large phyllosilicate content . Kaolinite and illite show good correlation with the abrasiveness index, while smectite decreases abrasion.

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.

Seven commercial cosmetic clays having different colour (white, green, pink and red) available in pharmacies and herbalists’ shops in the Greek market have been examined for their trace element concentrations (Ag, As, Ba, Be, Cd, Ce, Co, Cr, Cs, Cu, Ga, Hf, Hg, La, Mo, Ni, Pb, Rb, Sb, Sc, Se, Sr, Tl, V, Y, Zn and Zr). According to EC Regulation 1223/2009 the presence of As, Be, Cd, Cr, Hg, Ni, P, Pb, Sb, Se, Te, Tl, Zr and their compounds is prohibited in cosmetics. The most abundant trace elements in the white clays were P (330 μg/g), Pb (220 μg/g) and Zr (11 μg/g) and for the green clays were P (1250 μg/g), As (43 μg/g), Cr (31 μg/g), Pb (30 μg/g) and Ni (23 μg/g). Red and pink clays had lower concentrations of these elements than their white and green counterparts. The green clays are three times enriched in As and the kaolinite-rich white clays are nine times enriched in Pb compared to the Average Shale. The main mineral phase in the white clays is either kaolinite or calcite, in green clays smectite, in pink clay kaolinite and talc and in red clays it is vermiculite. The specific activities of 238U, 226Ra, 228Ra, 228Th and 40K were determined by γ-ray spectroscopy. The kaolinite-rich white clays are more enriched in 238U-series radionuclides (238U and 226Ra) than the smectitic green clays. In contrast, the green clays were more enriched in 232Th-series radionuclides (228Ra and 228Th) and 40K than the white clays.

This study examines the effect of German camomile (Matricaria camomilla L.) cultivation on the weathering of minerals present in the clay fraction of five different soil series modified or not unmodified (control) with cattle manure. A factorial experiment was performed in a randomized complete block design (RCBD) with three replications. At harvest time the rhizosphere soil was separated from bulk soil and the mineralogy was examined by X-ray diffraction (XRD). Trioctahedral chlorite transformed to hydroxy-interlayer vermiculite (HIV), while kaolinite disappeared. The presence of HIV was identified by an increase in the intensity ratio of the 1.0 and 1.4 nm peaks after Na-citrate pretreatment and K-saturation. It is suggested that Al3+ is released during dissolution of kaolinite and subsequently enters into the interlayer sheet of chlorite, and consequently the brucite layer disappears. This was verified by a significant Mg2+ increase in the soil solution in three out of five experiments at harvest time compared to pre-planting. The pots amended with manure showed the same changes as the pots without manure. The results of this study may explain the presence of unexpected clay minerals in regions with unsuitable conditions for their formation.

Trachyandesite rocks, occurring over an area of about 1 km2 in the southwest part of Limnos Island, Greece, are altered mainly to halloysite. The samples were collected and analysed by polarizing microscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and chemical analysis. The alteration of plagioclase to halloysite follows seven discrete stages that are described in detail. The geochemical evaluation of the data shows enrichment of the light REE (LREE) over heavy REE (HREE) as expressed by the (La/Yb)n ratio. The ΣLREE range from 206.44 to 272.30, while the sum of HREE varies from 11.01 to 26.26. The (La/Yb)n ratio ranges from 9.72 to 27.64. Fractionation among LREE expressed as (La/Sm)n and between middle REE (MREE) and HREE is shown as (Tb/Yb)n ratios. The most altered rocks close to the fault zone have high (Tb/Yb)n ratios and low (La/Sm)n and Eu/Eu* ratios. Although mineralogy and clay mineral textures indicate hydrothermal genesis of halloysite, the geochemical data are not conclusive due to a secondary weathering effect.

An Early Pliocene sedimentary succession in the Yenidoğan area, Sivrihisar, Turkey, consists of sepiolite, stevensite, kerolite, dolomite and magnesite. The geology, mineralogy and geochemistry of the succession was examined by extensive field work along several trenches and a representative measured section, followed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermal, and chemical analyses.

Structurally, two distinct forms of sepiolites were distinguished by XRD: (a) well crystallized sepiolite with a 110 reflection at 12.07–12.3 Å , and (b) poorly crystallized sepiolite in which the 110 reflection occurs at 12.7–13.0 Å (denoted as sepiolite-13Å ). Differences in crystal chemistry, thermal and morphological properties of these forms, the vibrational spectra and XRD characterization of the related phyllosilicates were also documented.

Stevensite, kerolite and sepiolite were formed by direct precipitation from alkaline lake water rich in Mg and Si. Sepiolite-13Å was probably formed by transformation from precursor smectite via dissolution-precipitation, more likely during early diagenesis. Environmental conditions such as ion concentration, salinity and variations in pH may have controlled the formation of the phyllosilicates.

Although investigation of the hydraulic conductivity behaviour of zeolite-bentonite mixtures (ZBMs) has been a topic of interest for researchers recently, the influence of compaction water content on the hydraulic conductivity of ZBMs has not been studied so far. This study discusses the hydraulic conductivities of ZBMs and compares the results with those of sand-bentonite mixtures (SBMs). The hydraulic conductivities of SBMs were unaffected by compaction water content and bentonite content, but the hydraulic conductivities of ZBMs were substantially different in mixtures containing 10% and 20% bentonite. The hydraulic conductivity of 10% ZBM (i.e. containing 10% bentonite and 90% wt. zeolite) gradually decreased as the water content increased to optimum water content and then it tended to decrease rapidly when the water content exceeded the optimum. In contrast, the hydraulic conductivity of 20% ZBM sharply decreased at the early stages of compaction water content (i.e. on the dry side of optimum water content) and levelled off when the water content was at the optimum water content. However, there is at least one order of magnitude difference between the hydraulic conductivities of ZBMs and SBMs, supporting the zeolite network model as suggested in previous works.