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Background. Ammonite products are increasingly gaining in popularity. Ammonites are characterised by a variety of colour shades, shapes and sizes, making them suitable for manufacturing a wide range of souvenir and jewellery products. Russia enjoys significant resources of ammonites of interior and jewellery-ornamental quality; however, these materials remain insufficiently studied from the mineralogical point of view. This article presents the mineral composition and gemological characteristics of the Upper Jurassic interior jewellery ammonites of the Samara region for the first time.Aim. To describe the stratigraphic position and mineral composition of interior jewellery ammonites of the Samara region.Materials and methods. Late Jurassic ammonites (45 samples) were collected from a number of their main locations. The characteristic types of ammonites of interior-jewellery quality were distinguished and studied. Experiments included the determination of microhardness (25 determinations), density (12 determinations), luminescence features (10 samples), optical and petrographic analysis (5 thin sections), as well as the quantitative determination of mineral and chemical composition (3 samples), and electron probe studies (2 samples).Results. Ammonites are characterized by the presence of a mother-of-pearl layer with multi-coloured iridescence. The ammonites under study consist mainly of apatite (21—70 wt. %) and calcite (21—87 wt. %) along with quartz, aluminosilicates, gypsum, pyrite, zeolites, goethite, ilmenite and organic matter. The chambers of ammonite shells are made of phosphorite and calcite. The walls and partitions of shells have completely lost their original aragonite composition and consist of apatite and calcite with pyrite inclusions. The increased content of Sr (up to 0.17 wt. %) and Ba (up to 0.01 wt. %) are recorded as trace elements in ammonites. Calcite contains the following trace elements (wt. %): Mg — 0.17, Mn — 0.17, Fe — 1.14, Sr — 0.11, and Y — 0.17.Conclusion. The mineral and chemical (including microinclusions and trace elements) composition of interior-jewellery ammonites was established for the first time. The ammonites of the Samara region are of commercial interest as interior samples. Their shell fragments can be used in jewellery production. The ammonites under study can be collected along the coastal cliffs and beach area of the Volga river, thereby requiring no capital investments and producing no environmental pollution.

For the first time, the mineral composition and structural features of jewelry ammonite from mine OJSC «Mikhailovcement» in Ryazan Region are studied in detail. Ammonites are associated with sediments of Callovian and Oxfordian stages. Ammonites have a complex zonal structure and mainly up to 96 wt. % pyrite composition. Aragonite, sulphates of calcium and iron, calcite, quartz, apatite, organic matter, graphite, ilmenite, feldspar, mica are established. The walls and partitions of the shells retain the original aragonite composition with lamellar and prismatic layers. Of the impurity elements, heightened contents are fixed (wt.%): As — up to 0,023 and Ni — up to 0,048, and in the range of 0,001—0,01 wt. %: Co, Zn, Mo, Sr, Ba and Pb. The content of radioactive elements U, Th are at the level of background with elevated levels of carcinogenic — As and Pb. The oxidation of pyrite and the formation of a number of micro-inclusions occurred presumably with the participation of bacteria. The main part of the shell is formed by densely fused pyrite crystals of 0,2—0,5 mm in size. There are fine-crystalline and globular pyrite, located on contact with aragonite layers of the walls and partitions of shells. In this zone, most mineral micro inclusions are located. According to their decorative and technological characteristics, ammonites are high-quality jewelry material of the biomineral group. The collection of ammonite shells can be carried out along the way with the development of a mine for the extraction of cement.

Detailed mineralogical examination of ammonites of jewelry quality has been carried out by means of radiographical, X-ray microanalyses and electronic microscopy. The ammonites consist mainly of calcite, apatite and some cells are constituted of phosphorite. The walls and shell’s septums consist of apatite and calcite, which have replaced original aragonite and maintain inclusions of pyrite of globular shape, aluminosilicate and organic matter. Dispersed apatite determines the black color of walls and shell’s septums. The color and transparency of the calcite, filling up the shell’s chambers, are determined by the quantity of micropores and microinclusions, mainly of apaTite. Ammonites from Kostroma region by its decorative and technology characteristics will be able to use widely in jewelry and interior articles.