Popigai Crater

The Popigai crater (or astrobleme) in Siberia, Russia is tied with Manicouagan Crater as the seventh largest verified impact crater on Earth. A large bolide impact created the 100 kilometres (62 mi) diameter crater 35.7 ± 0.2 (2σ) million years ago during the late Eocene (Priabonian stage). The crater is 300 km east from the outpost of Khatanga and 880 km (550 mi) NE of the city of Norilsk. It is designated by UNESCO as a Geopark, a site of special geological heritage.

Popigai is the best example yet of the formation of a crater of this type. Six other craters are larger; some are either buried (Chicxulub), strongly deformed (Sudbury), or deformed and severely eroded (Vredefort).

There is a small possibility that Popigai impact crater formed simultaneous with the approximately 35 million year old Chesapeake Bay and Toms Canyon impact craters.

For decades the Popigai crater has fascinated paleontologists and geologists, but the entire area was completely off limits because of the diamonds and the mines constructed by gulag prisoners under Stalin; however, a major investigatory expedition was undertaken in 1997 (IPEX 1997) which greatly advanced understanding of the enigmatic structure. The impactor in this event has been identified as either an 8 km (5.0 mi) diameter chondrite asteroid, or a 5 km (3.1 mi) diameter stony asteroid.

The shock pressures from the impact instantaneously transformed graphite in the ground into diamonds within a 13.6 km (8.5 mi) radius of the impact point. Diamonds are usually 0.5 to 2 mm (0.020 to 0.079 in) in diameter; a few exceptional specimens are 10 mm (0.39 in) in size. The diamonds not only inherit the tabular shape of the original graphite grains but they additionally preserve the original crystal's delicate striations.