Popigai impact structure

The Popigai impact structure is a massive geological feature in northern Siberia, Russia.

It is the eroded remnant of a giant crater. Scientists recognize it as the fourth largest verified impact structure on Earth. It is located east of the Khatanga outpost. The site sits northeast of the city of Norilsk and north-northeast of the Anabar Plateau. Because of its unique geological heritage, UNESCO has designated the area as a Geopark.

The structure was created by a massive bolide impact. A bolide is a large, bright object from space. This impact occurred approximately 35 million years ago. This time period is known as the late Eocene epoch. Specifically, it happened during the Priabonian stage. Some scientists believe this impact might be linked to the Eocene–Oligocene extinction event. There is also a small possibility that this event happened at the same time as the Chesapeake Bay and Toms Canyon impacts.

The mechanism that created the diamonds at Popigai is truly unique. The impactor was likely an H chondrite asteroid. This asteroid was thought to be several kilometers in diameter. When it struck the Earth, it created intense shock pressures. These pressures acted on the graphite already present in the ground. The shock instantaneously transformed the graphite into diamonds. This transformation occurred within a specific radius of the impact point.

The resulting diamonds have very specific physical characteristics. They inherited the tabular shape of the original graphite grains. They even kept the delicate striations from the original crystals. Most of these diamonds are quite small. They are usually about 1 millimeter in diameter. Many consist of nanodiamond agglomerates, which are tiny clusters of diamonds. However, a few exceptional specimens are larger in size.

Researchers have studied this site for many decades. For a long time, the entire area was completely off limits. This was because of the valuable diamonds found there. A major investigatory expedition finally took place in 1997. This expedition greatly advanced our scientific understanding of the structure. Scientists use ejecta layers from Italy to suggest the asteroid was an H chondrite. This helps them reconstruct the history of the impact.

One of the most fascinating parts of the site is the presence of lonsdaleite. Lonsdaleite is an allotrope of carbon with a hexagonal lattice. An allotrope is a different form of the same chemical element. Pure, laboratory-created lonsdaleite can be up to 58% harder than ordinary diamonds. The Popigai diamonds often contain this crystalline lonsdaleite. Scientists have even discovered carbon polymorphs at the site. These are combinations of diamond and lonsdaleite. These polymorphs are even harder than pure lonsdaleite.

These stones are scientifically known as "impact diamonds." They form when a meteorite strikes a graphite deposit at high velocity. While they are incredibly hard, they are not suitable for use as gems. Instead, they may have specific industrial uses. Despite their value, the diamonds have not been mined. The location is extremely remote and lacks necessary infrastructure. Additionally, these natural diamonds are unlikely to be competitive with synthetic diamonds.