The structure is 300 km (190 mi) east from the outpost ofKhatanga and 880 km (550 mi) northeast of the city ofNorilsk, NNE of theAnabar Plateau. It is designated byUNESCO as aGeopark, a site of special geological heritage.[5] There is a small possibility that the Popigai impact crater may have formed simultaneously with the approximately 35-million-year-oldChesapeake Bay andToms Canyon impact craters.[2]
For decades, the Popigai impact structure has fascinatedpaleontologists andgeologists, 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.[5] The impactor is suggested to have been aH chondrite asteroid based on ejecta layers from Italy, with the impactor thought to have been several kilometres in diameter.[6]
The shock pressures from the impact instantaneously transformedgraphite in the ground intodiamonds 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' delicatestriations.[5]
Popigai diamonds are about 1 mm in size and consist ofnanodiamond agglomerates.[7]
Most modern industrial diamonds are producedsynthetically. 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.[8] Many of the diamonds at Popigai containcrystallinelonsdaleite, anallotrope of carbon that has a hexagonal lattice.[9] Pure, laboratory-created lonsdaleite is up to 58% harder than ordinary diamonds.[10][8] 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.[9] They may have industrial uses but are unsuitable asgems.[11]
Additionally, carbonpolymorphs, a combination of diamond and lonsdaleite even harder than pure lonsdaleite, have been discovered in the crater.[12][13]
