The structure is 300 km (190 mi) east from the outpost of
Khatanga and 880 km (550 mi) 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.[6] 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 Canyon impact craters.[3]
For decades, the Popigai impact structure 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 structure.[6] The impactor is suggested to have been a
H chondrite asteroid based on ejecta layers from Italy, with the impactor thought to have been several kilometeres in diameter.[7]
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. These diamonds are usually 0.5 to 2 mm (0.020 to 0.079 in) in diameter, though a few exceptional specimens are 10 mm (0.39 in) in size. The diamonds inherited the tabular shape of the original graphite grains and also the original crystals' delicate
striations.[6]
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.[9] Many of the diamonds at Popigai contain
crystallinelonsdaleite, an
allotrope of carbon that has a hexagonal lattice.[10] Pure, laboratory-created lonsdaleite is up to 58% harder than ordinary diamonds.[11][9] 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.[10] They may have industrial uses but are unsuitable as
gems.[12]
Additionally, carbon
polymorphs, a combination of diamond and lonsdaleite even harder than pure lonsdaleite, have been discovered in the crater.[13][14]