Clay mineralogy and whole-rock chemistry of the borate-bearing layers of the Hisarcik and Esbey mines were examined. The Hisarcik clays occur as laminated or unlaminated clay layers with sharp contacts. Unlaminated layers contain quartz derived from metamorphic rocks and carbonate fragments in a clay matrix, and are interpreted as reworked tuffs deposited in playa-lake environments. An important feature is that the unlaminated clays contain little MgO (3–15 wt. %) as compared with the laminated clays (15–30 wt. %). As previous studies have shown, the clay fraction of the studied profile contains predominantly Li-bearing saponite, and accounts for 60–90 wt. % of the clay fraction (<2 μm). Illite in the clay fraction varies from 0 to 67 wt. % and the average illite percentage never exceeds 40 wt. %. Chlorite is scarce (2–5 wt. %). Illite-smectite interstratified clays (illite at 70%, smectite at 30%) were only found in low concentrations in the laminated clay layers of the upper limestone unit (above the borate zone), where illite-2M of detrital origin is also present. The Esbey clays occur interstratified with colemanite layers and envelope colemanite nodules. Calcite is the major mineral of the clays whereas quartz, plagioclase, feldspar, colemanite, and cahnite are minor components. The MgO contents vary between 4.70–13.95 wt. % in the clays interstratified with colemanite layers, between 7.24–11.89 wt. % in the enveloping clays, and between 10.27–21.25 wt. % in clays located above the colemanite zone. The composition of the clay fraction (<2 μm) in all samples is similar. Smectite represents between 40–90 wt. % of the clay fraction in the upper portion of the stratigraphic profile and decreases towards the lower part of the stratigraphic profile. Smectite always occurs with illite which may vary from 20 to 90 wt. % of the clay fraction, and a small amount of kaolinite and chlorite. Illite-2M polytype is abundant. The d(060)-reflection position suggests that the smectite minerals from the Hisarcik and Esbey colemanite mines contain both dioctahedral and trioctahedral smectites to form a transitional zone. These smectites are a product of a magnesium-rich alkaline playa-lake environment.

The aim of the aqueous electrokinetic experiments in the present study was to assess the relative contribution of the conducting polyindene (PIn) and inorganic colemanite components to the zeta (ζ) potentials of the composite particles, thus providing further insight into their surface composition in the dispersed state and establishing colloidally stable conditions for potential rheological, industrial applications. For this, PIn and a PIn/colemanite composite (containing 5 wt.% colemanite) were synthesized by chemical oxidative polymerization using FeCl3 as an oxidizing agent. Colemanite, PIn, and PIn/colemanite composite samples were characterized by Fourier-transform infrared spectroscopy, elemental analysis, conductivity, dielectric constant, magnetic susceptibility, density, particle-size measurements, thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction analysis, and scanning electron microscopy methods. The electrokinetic properties of colemanite and PIn/colemanite composite dispersions were determined by ζ-potential measurements in aqueous medium, taking into account the effects of time, pH, various electrolytes, surfactants, and temperature. The pH was observed to have a greater effect on the ζ potentials of colemanite in water but caused only slight changes in the presence of cationic (NaCl, BaCl2, AlCl3) and anionic (NaCl, Na2SO4) electrolytes. Increased pH values shifted the ζ potentials of PIn/colemanite composite dispersions to more negative values. The most effective surfactant acting on the ζ potentials of colemanite and PIn/colemanite composite dispersions was cetyltrimethylammonium bromide (CTAB), which shifted the ζ potentials to more positive regions. Elevated temperatures caused almost no change to the ζ potentials of either the colemanite or the PIn/colemanite composite dispersions.