They repel bad dreams, intensify love, counteract poisons, cure disease, thwart enemies, ward off wild animals and prevent natural disasters. They are, as the old ad(age) goes, forever.
The mythical powers of diamonds are, well, mythical. But there’s one diamond myth that contains a grain of truth: According to the Cape Town Diamond Museum website (which, for what it’s worth, is sponsored by a diamond seller, so take all romantic notions to follow with an appropriately-sized grain of salt), ancient Greeks and Romans believed that diamonds were pieces of falling stars. And, for a few, special diamonds, that is just about right.
Most diamonds that are mined on Earth formed more than a billion years ago, some 100 miles underground, where intense heat and pressure transformed carbon into diamond crystals. These buried diamonds made their way up to the surface via violent, long-ago volcanic eruptions, the thinking goes.
But that isn’t the only way to make a diamond. When two rocks — say, an asteroid and planet Earth — slam into each other, the pressure of the collision can shock carbon into diamond form. Diamonds can also grow up through the slow accumulation of carbon atoms, a process called chemical vapor deposition; this is how lab-grown gems used in jewelry are made.
Other than those “cultured” baubles, new additions to Earth’s diamond trove are rare. But on Oct. 7, 2008, scores of tiny diamonds fell to Earth, passengers on an asteroid that streaked over the Nubian Desert in Sudan.
The asteroid was remarkable, not just for the treasures hiding inside it, but because astronomers spotted it 19 hours before it skidded through the atmosphere: a first, which allowed astronomers to calculate its trajectory and pick out where the resulting meteorite fragments were likely to fall.
Soon, the asteroid struck Earth, a team of meteorite hunters, including a busload of students from the University of Khartoum, combed the search area, a zone near a remote train station called Almahata Sitta, or Station Six. They found dozens of pieces (today, the count tops 600), which gave researchers their first-ever chance to match up observations of an asteroid in space with meteorites on the ground.
Planetary scientists eagerly analyzed the rocks and found that many of them belong to a class of meteorites called ureilites. Ureilites are nearly black, rich in carbon and very porous. Some planetary scientists think that all ureilite meteorites come from one original parent body, though no such parent rock has ever been found.
Now, by examining the diamonds within the Almahata Sitta meteorites, planetary scientists are deciphering the nature of that parent body. Because the diamonds within the Almahata Sitta meteorites were so big — about a tenth of a millimeter across, stunning by asteroid standards — they could not have formed via a swift impact or chemical vapor deposition, the researchers argue.
The researchers also found minerals trapped inside the diamonds, similar to the imperfections inside terrestrial gems. Taken together, these features point to a scenario in which the Almahata Sitta diamonds crystallized very much like Earth diamonds: buried deep, under high, sustained pressure.
This suggests that the Almahata Sitta meteorites, as well as other ureilites, come from a long-lost protoplanet, a rock bigger than Mercury and smaller than Mars. That makes Almahata Sitta fresh, hold-in-your-hand evidence for the notion that our solar system’s rocky planets fused through a series of smashups among Mars-sized rocks. The rock that the ureilites comes from probably broke up about 4.5 billion years ago, the researchers conclude.
So, maybe the Greeks and Romans were on to something. As for bad dreams, wild animals and everlasting love? You’ll have to do your own experiment.
Kate Becker is a science writer living in Boston. Contact her at spacecrafty.com, or connect via facebook.com/katembecker or twitter.com/kmbecker.
