This is from a famous fossil deposit of 300-million-year-old Ammonites along the Volga River in Russia (Jurassic Callovian Stage-161 million years ago). After burial, the original ammonite shell material was partially converted by mineralizing fluids rich in iron and sulfur into pyrite. The sliced fossil now reveals an awesome view of living chambers of the ammonite coated with splendent brassy yellow pyrite. each piece is approx., 6.3 x 5.1 x 1.0 cm, almost similarly sized. This ammonite is Quenstedticeras species. While I do not deal in a lot of fossils per se, I have seen these over the years and this particular set was, to my eye, just incredibly appealing as a dual fossil and mineral specimen with its high quality pyritization and aesthetic balance.