Editor's note: A version of this was previously published on the author's blog.
By definition, anything superlative is the most-whatever of its type; the coldest winter, the greatest rainfall, the highest mountain. It's unique, untouchable among its kind. The tiny Hypatia Stone is such an object. It's the strangest rock on Earth.
In December 1996, Aly A. Barakat, a researcher with the Geological Survey of Egypt, was in the southwestern section of his country participating in an Egyptian-Italian expedition to the site of "Lybian desert glass." The glass is an unusual yellowish material now thought to have formed from a high-pressure impact, such as a meteorite or asteroid strike, on desert sand. A pebble about an inch long, an inch wide and a little thinner than an inch caught his eye because it didn't look like other rocks in the area.
Partly buried in the dirt, it was shiny gray-black and weighed just over an ounce. At first Barakat thought it might be a tektite. A tektite is a stone formed by the melting of rocks hit by meteorites and their subsequent cooling, according to the Encyclopedia Britannica. However, examination in the field showed it was not. It was something more peculiar.
The pebble was studded with microscopic diamonds, he discovered.
Diamonds typically form in the Earth's mantle about 90 miles underground in super-hot and super-pressurized conditions, where naturally present carbon deposits are squeezed and heated. (Coal is not involved.) Later, volcanoes may shove diamond-bearing formations to the surface. Also, diamonds form through the impact of asteroids — the enormous pressure and heat of the strikes are enough to do the job. And microscopic diamonds called nanodiamonds have been discovered in meteorites, the result of high-speed collisions of rocky debris in space.
Small pieces of the stone were examined independently in labs in Egypt, Italy and South Africa. "All these studies proved that the material contains the first record of tiny grains of diamond in Egypt," Barakat wrote at drbarakataly.wordpress.com.
He said the material is dubbed the "'Hypatia Stone' after Hypatia of Alexandria (c. A.D. 350–370 – A.D. 415) the outstanding woman philosopher, astronomer, mathematician and inventor."
Major contributors to our understanding of the matter are Jan Kramers and Gregory Belyanin of the University of Johannesburg, South Africa. Their university reportedthat they "found exotic micro-mineral compounds in the 'Hypatia' stone that are not known to occur on Earth, elsewhere in our solar system, or in known meteorites or comets."
In a paper to be published officially on Feb. 18 by the journal Geochimica et Cosmochimica Acta, but whose abstract is already available on line, Kramers, Belyanin and colleagues wrote that their extensive studies indicate the material is of "pre-solar origin."
A 2013 study by the group posited that the stone might be a remnant of a comet's nucleus. But Kramers told The Evening News in a Jan. 18 email, "We have now found that it does not contain any silicates at all (except in the fractures, where minerals of terrestrial origin have formed, such as clay minerals). All studied cometary material (interplanetary dust particles and in situ collected dust from NASA's Stardust mission) has silicate minerals."
"Further there are exotic minerals which we think must be presolar, such as silicon carbide, a nickel phosphide compound with extremely high Ni/Fe (nickle to iron) ratio (around 80) that cannot be formed in the solar nebula by any process, and grains of metallic zinc, aluminium (which we Americans call aluminum), iron and silver. …
"All in all we now think that the stone's parent body formed by dust agglomeration in the outermost solar nebula and remained cold until its encounter with Earth."
Kramers doubts that the stone is a wanderer from another star system, like the asteroid or comet spied flying through our own in October, which NASA says originated from elsewhere in the galaxy.
"We don't think that the object comes from outside the solar system because its xenon isotopes are similar to those of carbonaceous chondrites," he wrote. Carbonaceous chondrites are a rare type of meteorite. "But it certainly contains extrasolar dust. One important conclusion is that the solar nebula was primarily not quite homogeneous, containing regions without silicate grains."Comment on this story
Dating to more than 4.5 billion years ago, the Hypatia Stone is a relic of a period around the time the solar system condensed from a vast interstellar cloud of hydrogen, nitrogen, carbon, dust and other molecules. As elsewhere in space, this cloud was seeded with elements from previous generations of stars that went supernova.
The new study indicates that this strangest rock comes from the nebula that was clumping up before the solar system finished condensing. And now we know that elements were not distributed evenly in the cloud.