Simbircite from the Russian city of Simbirsk is another one of those jaw-dropping gemstones that leave everyone speechless. They are beautiful, rich and understated. It is an agatized material that fills in chambers of the Ammonite Lamberticeras sp. with a complex mix of magnesium rich calcite, aragonite, pyrite, marl, chabazite and quartz. The veins of pyrite were originally the bone of the ammonite. Formed over millions and millions of years, Simbercite with pyrite is both a gemstone and fossil.