The pieces closely resemble regular brownish-black earth rocks to the untrained eye.
A Boston auction house is offering what it says is the largest chunk of moon rock ever put up for auction, a rare lunar meteorite that was discovered in northwest Africa.
The meteorite comes in six pieces that fit together, weighing a total of about 12 pounds (5 kilograms), and has a sale estimate of $500,000 in the sale closing October 18, RR Auction said.
"It is one of the larger lunar meteorites ever found," Geoff Notkin, the chief executive officer of Aerolite Meteorites, the company selling the specimen, said in an interview. "And there's never been one like this and we call it a lunar puzzle."
Although the pieces closely resemble regular brownish-black earth rocks to the untrained eye, Notkin said it was a thing of rare beauty to a meteorite aficionado such as himself.
Some pieces of moon rock have made their way back to earth in the care of Apollo astronauts. The rest were blasted off the moon's surface by meteorite impacts, typically hundreds or thousands of years ago, blazing through earth's atmosphere like a shooting star.
Most likely disappear into the planet's oceans, but a few hundred confirmed examples of lunar meteorites have been found in recent decades on land, many in Antarctica or the deserts of northwest Africa.
In 2012, Heritage Auctions offered what it said then was the largest chunk of moon rock ever come to up for auction, weighing about 4 pounds (1.8 kg).
Even the largest single fragment of the Aerolite specimen, known as Northwest Africa 11789, appears to be bigger, weighing over 4.4 pounds (2 kg), according to its entry in the Meteoritical Bulletin Database run by the Meteoritical Society, a non-profit group based in Virginia.
The database entry says the meteorite is composed of nine pieces, not six.
"I'm pretty sure it was a mistake," said Dustin Dickens, the meteorite trader who submitted the entry after purchasing the specimen last year in Mauritiana from a meteorite hunter he said wanted anonymity after finding the pieces in neighbouring Mali.
He believes it was seven pieces, but said he gave the smallest piece, weighing a few dozen grams, to the University of New Mexico's Institute of Meteoritics for testing.
Notkin and RR Auction did not immediately respond to questions about the discrepancy.
In 2007, one of the largest lunar meteorites ever found was discovered in Morocco, a single lump weighing 25 pounds (11.5 kg.)