Sergo Ordzhonikidze Russian State Geological Prospecting University, Moscow, Russia:

D. A. Petrochenkov, Associate Professor, Candidate of Geologo-Mineralogical Sciences, p-d-a@mail.ru

Manufactured articles of ammonites have been in increasingly higher demand in the recent decades. Ammonites have appeal for the unique shapes, color and age. The top suppliers of ammonites to the world market are Madagascar, Morocco, Canada and Russia. In Russia, gem-quality ammonites occur in the Saratov Region, apart from other places. The regional open pit mine at the settlement Dubki situated 7.5 km northeastward of Saratov supplies ammonites both to the Russian and global markets. The submicroscopic and electron microprobe analyses presented details of mineral composition and structure of ammonite shells. The test shell fragments included walls and partitions with layers of pyrite. The pyrite layers lay symmetrically relative to the partitions and inside walls of ammonite, and feature pronounced structural zonality. The partitions and walls are adjoined with narrow zones of fine-crystal pyrite. Then, a zone of coarse-crystal pyrite lies, with fragments of colloform pyrite. The gem-quality ammonites have mostly pyrites in their composition (to 96 % by mass) and are connected with the Upper Jurassic deposits. Among other things, ammonites contain aragonite, calcite, apatite, jarosite, gypsum, ferrian carbonate and organic substance. The original aragonite is preserved in walls and partitions of shells. Morphologically, the large prismatic, fine-crystal, colloform and globular species of pyrite are distinguished. Pyrite is actively decomposed by bacteria. The Saratov Region ammonites possess high decorative and processing properties, can be widely used in manufacturing of jewelry and are by-produced in the course of large-scale mining.

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