The Popigai crater in Siberia, Russia, is tied with the Manicouagan Crater as the fourth largest verified impact crater on Earth. A large bolide impact created the diameter crater approximately 35 million years ago during the late Eocene epoch. It might be linked to the Eocene–Oligocene extinction event. The crater is east from the outpost of Khatanga and northeast of the city of Norilsk, NNE of the Anabar Plateau. It is designated by UNESCO as a Geopark, a site of special geological heritage. There is a small possibility that the Popigai impact crater may have formed simultaneously with the approximately 35-million-year-old Chesapeake Bay and Toms Canyonimpact craters. For decades the Popigai crater has fascinated paleontologists and geologists, but the entire area was completely off limits because of the diamonds found there. However, a major investigatory expedition was undertaken in 1997, which greatly advanced understanding of the enigmatic structure. The impactor in this event has been identified as either an diameter chondriteasteroid, or a diameter stony asteroid. The shock pressures from the impact instantaneously transformedgraphite in the ground into diamonds within a radius of the impact point. These diamonds are usually in diameter, though a few exceptional specimens are in size. The diamonds not only inherited the tabular shape of the original graphite grains but they additionally preserved the original crystals' delicate striations.
Diamond deposits
Most modern industrial diamonds are produced synthetically. The diamond deposits at Popigai have not been mined because of the remote location and lack of infrastructure, and are unlikely to be competitive with synthetic diamonds. Many of the diamonds at Popigai contain crystallinelonsdaleite, an allotrope of carbon that has a hexagonal lattice. Pure, laboratory-created lonsdaleite is up to 58% harder than ordinary diamonds. These types of diamonds are known as "impact diamonds" because they are thought to be produced when a meteorite strikes a graphite deposit at high velocity. They may have industrial uses but are unsuitable as gems. Additionally, carbon polymorphs even harder than lonsdaleite have been discovered in the crater.
