While it’s a truism that not all diamonds are created equal, recent scientific research suggests that sometimes, the differences go far deeper than most diamond aficionados might expect. Take carbonado diamonds, for instance. These black stones, which look like chunks of porous charcoal, are among the rarest diamonds on Earth. Now we know why: they’re not from around here. And we mean really not from around here.

Given their porosity and great rarity, natural carbonado diamonds have limited use in jewelry manufacture; however, they work great as tiny time capsules, locking up chemicals and gases that can tell scientists where and when they originally formed. A recent analysis of their chemical makeup makes it clear that carbonado diamonds were cooked up in the depths of outer space, probably as the result of massive supernova explosions: in other words, they’re the cinders left over after giant stars die violently. Their extraterrestrial origin was revealed in an article published in December 2006 by geologists based at Florida International and Case Western universities.

At their most basic, diamonds are nothing but structured carbon, one of the most common elements in existence. We humans beings, and in fact all living things, include a high percentage of carbon in our chemical make-up. Similarly, coal, soot, and graphite are all forms of carbon; it just so happens that when carbon comes together in the right way, in the presence of tremendous head and pressure, it can form a rigid latticework harder than anything else we know of.

Normal diamonds are formed when masses of explosive, carbon-laced magma (molten rock) is thrust upward from many miles below the surface of the Earth, into cooler sections of the crust where it hardens into a type of rock known as kimberlite (after Kimberly, South Africa, where it was first formally identified). This process follows certain natural laws that are the same all over the world, producing diamonds with essentially the same chemical and physical structure, whether they’re mined from Arkansas, Russia, South Africa, India, or Brazil. As the diamonds form, they often trap other materials in the crystal latticework, forming pockets of impurities (much to the dismay of the jewelers who later examine them). Perhaps the most common inclusion is nitrogen, the principal component of our atmosphere, which conspires to make most diamonds some shade of brown or yellow.

Hydrogen, which comprises two-thirds of the chemical mix that forms water, is very rare in earthbound diamonds. However, it happens to be the most abundant chemical element in the universe, and is extremely common in space. Most of the interstellar dust clouds, or nebulas, that we ooh and aah over in astronomical photos are made up of hydrogen, spewed out in massive star explosions and lit by the dying remnants of those stars. According to theory, the enormous heat and pressure generated in those supernovas is sufficient to form diamonds in deep space — and the new study suggests that this did, in fact, happen. The carbonados we know and love are the result. As it turns, out, the nitrogen and hydrogen densities inside carbonado diamonds closely match the composition of hydrogen-rich nebulas in space. It’s pretty obvious, then, that natural black diamonds are the charred bones of burnt-out stars.

It’s theorized that the primordial chunks of carbonado diamond were huge: they would have been the size of asteroids — a half-mile or more in diameter — and weighed millions of tons. As some point in the distant past, one or more of these adamantine asteroids fell to Earth, possibly breaking up in the process. Erosion took care of the rest, rendering the remnants down into fragments small enough to be scattered by running water. Today, carbonado diamonds are found only in limited alluvial settings in Central Africa and Brazil. Although most diamonds are mined from similar settings, minors have never recovered a carbonado diamond from a normal diamond mine, which tends to confirm their unique origins.