"It's interesting how you price meteorites," said James Hyslop, a specialist at Christie's London who's organised an April 20 sale of 76 meteorites, pointing to meteorites' scarcity and the fact that available stock is only occasionally replenished (the 2013 Chelyabinsk meteor explosion over Siberia added significantly to available material). "It can really be quite difficult."

Partial slice of imilac meteorite with peridot, estimate: £2,000-£3,000. Photo: Christie's

Historically, meteorites were valued by gram, Hyslop said. The heavier they were, the more expensive. (See: James Bond's Spectre for a $US600,000 example.) Recently, however, collectors have begun to take both aesthetic and historic aspects into consideration. "The diamond industry uses the four C's," said Hyslop. "We use the four S's: size, shape, science, and story."

Size and shape

Size is obvious-more meteorite, more money; shape, less so.

"When most meteorites fall to earth, they tumble chaotically," Hyslop explained. "You don't have them plowing straight down." On the rare occasion a meteorite does head straight into the earth, its surface heats, then melts, and "you get this wonderful heat shield that has a perfect parabola to it." Parabola-shaped meteorites, in turn, are much more expensive.

An oriented Chelyabinsk meteorite. Photo: Christie's

Science and story

The scientific aspect of meteorite valuation is more complicated, and is often combined with its story.

"Some of the most sought-after ones are the pallasite slices and spheres that have peridot," Hyslop said, referring to the greenish gemstone. "Others, like the lunar meteorite, are always incredibly popular." By lunar meteorite, Hyslop is referring to an actual piece of the moon that was blown into outer space by the impact of a much larger meteorite there, floated around for possibly millions of years, and then happened to collide with the earth. There's even a couple martian meteorites from, you guessed, Mars.

"I still get a childlike excitement when I hold a piece of another world in my hand," he said.

A lunar meteorite (feldspathic, regolithic breccia) found in the Sahara Desert, northwest Africa. Photo: Christie's

The estimates

Seven more lots that offer research notes and ephemera from the archives of a famed 19th century meteorite dealer round out the sale. Estimates for the 83 lots range from $US355, the high for a corner-cut of the Toulon meteorite, to more than $US1.1 million for the world's largest "oriented" meteorite (which means it has that parabola shape) embedded with extraterrestrial gemstones.

"If you were to cut a slice through it, you'd see this iron matrix of olivine crystals, some of which are so high-quality they're technically gemstones," Hyslop said.

Many of the meteorites come from long-standing private collections, while others come from museums that exchanged slivers of their existing meteorites for new "incredibly rare" meteorites, Hyslop said. One lucky collector at the Christie's sale will be able to buy a piece of the Willamette meteorite, currently on display at New York's American Museum of Natural History (estimate: $US99,470 to $US142,100).

An anthropomorphic Gibeon meteorite. Photo: Christie's

Hyslop has seen advance interest from around the globe.

"It's a nice international crowd," he said. "Not just the traditional meteorite collectors, but from the international art market, too."

If meteorite buyers have one thing in common, it's their gender: "I'd hazard a guess that about 75 per cent of them are male."

Bloomberg