Mg clay minerals are usually associated with carbonates in alkaline-saline environments, precipitated from solution and/or transformation from other minerals. The aim of this research is to identify the mineralogy and geochemistry of clay minerals in different alkaline lakes in the Nhecolândia region, the southernmost region of the Pantanal wetland (Brazil). Sediment samples were analyzed by X-ray diffraction, X-ray fluorescence, scanning electron microscopy and transmission electron microscopy. Water samples were analyzed, determining their main cations and anions, in order to understand their relationship with the clays. The analyses allowed classifying the water bodies as saline, oligosaline and freshwater lakes. The sediments are composed mainly of quartz and a fine-clay fraction, dominated by illite, kaolinite and smectite. The XRD results showed illite and smectite mixed-layered in the saline lakes at Barranco Alto farm, whereas at Nhumirim farm, trioctahedral smectite was only observed in one lake. The smectite minerals were normally identified coupled with calcite at the top of the sequences, associated with exopolymeric substances (EPS) in the lakes, suggesting that these minerals are precipitating due to the physical-chemical and biological conditions of the water bodies.

Kidney stones are precipitated when abnormal conditions within the urinary tract promotes local ions supersaturation, changes in the pH, and, in some cases, a differential bacterial influence. The most common minerals in kidney stones are calcium oxalates, followed by calcium phosphates, struvite, cystine and uric acid. In this study, the morphological and mineralogical characteristics of kidney stones were registered and applied to simplify their identification and facilitate the diagnosis. Furthermore, we performed isotopic analysis to verify the likelihood of external factors influencing kidney stones formation. In total, 160 samples of kidney stones from different patients above 18 years old were analyzed. We examined the morphological characterization macroscopically, based on features such as color, fabric and relative hardness. The x-ray diffraction (XRD) applied to mineral identification indicated that whewellite was present in 64% of the samples, followed by 14% uric acid stones and 10% struvite stones. The x-ray fluorescence (XRF) revealed that the majority of the kidney stones were formed by phosphates and calcium oxides, followed by magnesium, sodium and sulfur oxides. Isotopic analysis showed δ13C values from − 23 to -8‰ and δ18O values between − 12 and − 6‰ in different types of kidney stones. All the results have shown that it is possible to improve the discrimination of kidney stones based on some morphological features associated with chemical and isotopic composition. Furthermore, isotopic results have suggested that kidney stone formation can be associated with different diets and water intake.

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