Jewelry and ornamental concretions with fossils of the Republic of Kabardino-Balkaria. Mineral composition, gemological characteristics

Background. Along with ammonites and septaries, concretions with fossils are increasingly being used as jewelry and ornamental materials in Russia. Such concretions are characterized by a wide range of sizes, as well as high decorative and technological properties, making them attractive materials for manufacturing diverse interior and jewelry products. The collection and processing of concretions with fossils was previously carried out in the Ulyanovsk region. In this paper, similar concretions found in the Republic of Kabardino-Balkaria are studied for the first time.Aim. Tо establish the stratigraphic position, mineral composition, and decorative and technological characteristics of concretions with fossils of jewelry and ornamental quality found in the Republic of Kabardino-Balkaria.Materials and methods. The collection sites of concretions with fossils and their stratigraphic position were studied. In total, 15 samples characterizing the main decorative and technological types were selected. Interior and jewelry items were manufactured from the concretions; typical samples were studied. A set of studies included the determination of luminescence (8 samples), microhardness (8 cycles), density (6 cycles), optical-petrographic analysis (3 sections), quantitative determination of mineral and chemical composition (2 samples), electron probe studies (2 samples).Results. Concretions with fossils of commercial quality are associated with lower Aptian deposits, representing marlstone with a large number of shells, mainly ammonites, and, to a lesser extent, bivalves. These comprise (wt %): calcite — 64.0, quartz — 18.7, microcline — 7.4, illite — 5.6, smectite — 2.7, kaolinite — 1.0, strontianite — 0.5, as well as traces of pyrite, apatite, albite, ilmenite, and goethite. Among the impurity elements, Sr in the amount of 0.0402 wt % is recorded.Conclusions. For the first time, the mineral and chemical (including micro-inclusions and impurity elements) composition of concretions with fossils of jewelry and ornamental quality are established. Factors determining their decorative and technological characteristics are identified. The possibility of using concretions with fossils for manufacturing a wide range of products, including jewelry, is shown. Concretions can be collected simultaneously with ammonites and septaries in river valleys without mining, thereby involving minimal costs and having no negative effect on the environment.