The far reaches of Siberia are famous for the numbers of meteors which they seem to attract. Many know about the famed “Tunguska event” of June 30th, 1908, which leveled hundreds of square miles of forest, killed thousands of deer, broke windows 50 miles away and which has never been explained to everyone’s complete satisfaction.
More recently in February of 2013, the people of Chelyabinsk were treated to a colossal explosion caused by a meteoric intruder which broke an estimated million panes of glass and injured 1,200 people.
But these explosions, colossal though they may have been, were small fry compared to that caused by the chunk of space rock that struck what is now Russian Siberia nearly 35 million years ago. Along with flash cooking Andrewsarchus, Brontotherium and other alien fauna endemic to the Siberia of the late Eocene, this extra-planetary traveler also blew a 63-mile-wide hole in the ground which is now known as the Popogai Crater, the seventh largest known such crater on Earth at this time.
The Popogai crater has something else unusual about it besides its great size. It is also filled with remnants of that monumental explosion in the form of millions of diamonds. These particular gems are called impact diamonds because they were formed by the enormousl heat and pressure generated by the meteor strike working on carbon.
Transmutations of this order are common when such events occur. Silicon is changed into volcanic glass. Quartz morphs into an iron-based crystalline mineral called siderite, and so forth.
In the case of the Popogai diamonds there happened to be large natural deposits of graphite, a form of carbon that forms sheets of hexagonal crystals, present in the soil. When the meteor struck, the environment was momentarily transformed where carbon was subjected to pressures in excess of 20 gigapascals. To put that in perspective, that is over 100 times the pressure exerted by water at the deepest spot in any of the oceans: the Marianas Trench.
The heat generated by the strike would necessarily exceed that of a deep magma well, where terrestrial diamonds form. It would, in fact, momentarily exceed temperatures that exist at the surface of the sun.
The Popogai diamonds and to a lesser extent those at all similar craters - which generally lacked Popogai’s unusual graphite deposits - come in grades of diamond varying from first water gemstones to industrial grade stones called lonsdaleite, which are a form of hexagonal crystalline diamond possessing the rare and highly desirable property of being 58 percent harder than mere diamond, formerly the hardest known naturally occurring structure on earth.
Popogai Crater, according to its Russian owners, is home to not billions, but trillions of carats of diamonds of all descriptions, including most of the lonsdaleite known to exist.
Those are the conditions needed to produce impact diamonds; extreme heat, extreme pressure and a source of carbon. Once present, the resulting diamond deposit, unlikely ever to be as spectacular as that at Popogai, is inevitable.