The crystallographic directions of the crystal toward the vector of polarized light can accurately be positioned, so the information that we gain from polarized spectra can be consistently interpreted according to known crystal structure. The orientation and optical properties of the methylene blue (MB) crystals were analyzed by XRD, XRPD, and polarized VIS-NIR spectroscopy. Cationic dye, MB, was polymerized into crystals on a glass slate. The blue color crystals showed pronounced dichroism, twin lamellar structure and bladed to fibrous habit. According to XRD data, [010] direction lies perpendicular to the crystal surface, so we recognized it as (0k0) face, while [100] and [001] directions coincide with crystal elongation and crystal thickness respectively. In this paper, the polarized spectra of MB crystal are presented, measured with the aim of acquisition of referent values, which could be helpful for the identification of MB molecular aggregation.

The present study focused on the assessment and possible applications of the clay from the Miličinica deposit, western Serbia. X-ray diffraction (XRD), Infrared (IR) spectroscopy, Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), Differential Thermal Analysis and Thermogravimetry (DTA-TG) and High Temperature Microscopy (HTM) were used to characterize the clay in question. The physical properties determined were colour, plasticity, specific surface area, particle-size distribution and cation exchange capacity (CEC). Clay minerals are the main phases in the samples studied, with illite being the predominant phase and kaolinite being present in variable amounts. Quartz, feldspars, carbonates and iron-bearing minerals were also detected. Varied technological behaviours were expected because of the mineralogy (illite and iron contents), average grain size (0.6–0.7 µm), specific surface area (≈60 m²/g) and plasticity index (≈13%). The classification of the clays studied, based on the main characteristics and using appropriate diagrams, suggests that they are easily adaptable for ceramic processes.

This study focuses on the mineralogical characterization of four raw clay samples from Dobrodo deposit, Serbia. Several analytical methods were applied to determine the chemical and mineralogical composition, morphology and physical properties (colour, plasticity, specific surface area, particle size and cation-exchange capacity) of the clay samples. Kaolinite, smectite and illite are the predominant phases in all of the samples studied that contain between 60.2 and 87.1 wt.% of clay. Quartz, feldspars, paragonite and Ti- and Fe-bearing phases were also identified. The relatively high SiO₂/Al₂O₃ mass ratio indicates abundant quartz. The cation-exchange capacity of the samples varied between low and moderately charged clay minerals (12–52 mmol 100 g^–1) with specific surface area values ranging from 94 to 410 m² g^–1. The plasticity index values (11–23%) suggest low to moderate plasticity. Preliminary results show that most of the raw clay from Dobrodo deposit might be suitable for use in ceramic applications.

Five celestine crystals were sampled from the (palaeo)surface intervening between the late Miocene to Pleistocene basaltic sequences of the Jabal Eghei (Nuqay) volcanic province in southern Libya and then characterised by applying a combination of the SEM–WDS, ICP/OES, PXRD and IR methods. Colour variations and related minerogenetic frameworks were also investigated. Three samples have greenish-blue-to-blue colour (480.4–482.5 nm), whereas the other two samples have blue–green colour (cyan; 489.1–494.1 nm). The colour purity ranges from 1.36–7.16. Their composition is similar, end-member celestine, in which only 1.6–4.1 at.% of Sr²⁺ content was substituted by Pb²⁺ (0.7–0.9 at.%), Ba²⁺ (0.5–0.7 at.%) and Ca²⁺ (0.2–0.8 at.%). Three samples contained vacancies, from 1.0 to 1.9 at.%. The content of other chemical elements is minor. The resulting unit-cell parameters have the ranges: a₀ = 8.3578(9)–8.3705(6) Å; b₀ = 5.3510(5)–5.3568(4) Å; c₀ = 6.8683(7)–6.8767(2) Å and V₀ = 307.17(5)–308.34(4) ų. The PXRD and IR results are mainly in accordance with the SEM–WDS results, with a high level of correlation. However, a few discrepancies were found, producing several possible interpretations, the primary cause being a slight unit-cell axial anisotropy i.e. thermal expansion. As a consequence these results yield a new geothermometric tool that is based on the unit-cell axial anisotropy. The celestines investigated were formed during a Miocene intraplate volcanism with basaltic magmas, and associated brines lifted by the structural conduits (normal faults crosscutting the Sirt basin). The Sr-bearing fluids then poured into and over the faulted and fractured lagoon-type gypsum, anhydrite Eocene sediments. The celestine mineralisation formed within a ~368–430 K (~95–157°C) temperature range. The celestine formed at slightly elevated temperature and pressure conditions, close to the shallow subsurface environment (over 250 bars).