Professional meteorite hunters were quickly on the scene last week after a large space rock entered the atmosphere over the Russian city of Chelyabinsk and exploded. Demand from international collectors is such that a tiny fragment of the meteorite could fetch hundreds of dollars. Reports have already surfaced on Russian websites of pieces being offered for sale for as much as £6,500.
But how do you tell that what you are buying is a genuine meteorite and not, say, a piece of painted concrete?
“The first thing to look for is the ‘fusion crust’,” says Dr Natalie Starkey, a cosmochemist at the Open University who specialises in the study of meteorites. “Think of what the crust on baked bread looks like. The exterior of the meteorite will be shiny, smooth and black. The heat generated by entering our atmosphere causes the rock’s exterior to melt like glass. This appearance is a good indicator that it’s a meteorite, but, sadly, it isn’t definitive. Ultimately, it will need forensic examination by an expert.”
The British and Irish Meteorite Society warns on its website that there are a “few unscrupulous salespeople around who may be selling terrestrial rocks as meteorites”. It advises to first do your homework about the various types of meteorites and then to only buy from a reputable dealer, ideally one that is a member of the International Meteorite Collectors Association. It adds: “Meteorite-Identification.com is a good source of information on suspect eBay auctions.”
“The only way to tell for sure is to look at the specimen under a microscope,” says Starkey. “Some minerals, such as biotite, only form on Earth. A specialist will be able to identify those and then rule out whether it’s a meteorite. The only truly definitive test, though, is to examine the specimen for oxygen isotopes. Anything that originated on earth will fall within a particular range of isotopes. Anything outside this range will mean it is extra-terrestrial in origin.”
Starkey says events such as the Chelyabinsk meteorite are rare and only occur once a year, on average. It is near-unique, though, that its descent was captured on camera. This will only add to the price of any fragments offered for sale, she says: “It appears to be a fairly normal meteorite from the asteroid belt – what we call an ordinary chondrite. If it had originated from Mars, though, it would be far rarer and command an even greater price among collectors. Even so, this will be big business for the meteorite dealers.”