Meteorites are an extraordinarily valuable natural commodity, with the rarest kinds worth far more by weight than gold or any other material you are likely to find.
The key to this is the combination of wonder that material all the way from outer space can inspire and the extreme rarity of the examples. Meteorites - fortunately - don't fall to Earth very often.
Those that do fall are often easy for the untrained eye to overlook, and unless there is an unexplained crater nearby, it's not always obvious where to search.
The strong financial value of meteorites was demonstrated earlier this year when a Russian smuggling ring was discovered to have included rare spacerocks in their portfolio of illegal goods. Here we take a look at our top five most collectible kinds.
Most meteorites which fall to Earth are stony chondrites (composed of grains typically brought together in space to form a larger object), and meteorites which are high in iron are relatively rare - though easier to spot for the lay man.
It has been claimed that Attila the Hun fashioned his beloved sword from an iron meteorite.
Although not the very rarest, or most valuable by weight, iron meteorites such as octahedrites are often the most imposing and simply the largest pieces which appear at auction or in museums. Notably, the Willamette meteorite of Oregon is simply astounding.
One of the Bonhams' biggest meteorite sales was an aesthetic octahedrite - a 99kg Sikhote-Alin from Siberia, once part of the Macovich collection. The fascinating piece, its surface changed by its descent through our atmosphere, brought $122,750.
Angrites are completely different from octahedrites. Only pieces sized a few grams ever make it to auction and the dark, rocky pieces are neither gleaming nor sculpted, though sometimes the dark colours reflect a slight glimmer when turned in the light.
The extremely rare pieces are thought to have originated on Mercury, the closest planet to the Sun, and been scored from the surface by the impact of another space rock, though it's impossible to be certain that they haven't come from another body near the Sun.
Earlier this month, a 9g dark, purple-and-greenish-brown angrite sold at Bonhams for $6,710 - well above its estimate.
Impacts on the moon also very occasionally launch material out into space, which also might come to Earth. Lunar meteorites come in a few different forms depending on, for example, from how deep the rock originated.
It's possible to be sure that lunar meteorites originated on the moon because they can be tested against the samples that the 12 moonwalkers of the Apollo missions brought back from there.
Heritage Auction Galleries sold a lunar meteorite for $42,661.50 in 2008, and a 4.26g piece sold for $11,350.50 just a week ago.
Pallasites are universally acknowledged as the most beautiful meteorites in existence. Consisting of an iron-nickel matrix with bright green olivine 'spacegems' embedded in it, a pallasite is recognisable immediately as sometimes out of the ordinary - something other-worldly.
Surprisingly, the man who first discovered a fallen pallasite, naturalist Simon Pallas, is lucky to have his name attached to them as he was opposed to the idea that they came from Space.
The exact source of pallasites is disputed, but their mesmerising appearance is not and they are often used as a centrepiece in museum displays.
Last week, a 1kg slice of the Imilac pallasite (from a fall in Chile) which had been part of the Macovich collection, and even the Museum of Natural History in Britain, sold for $23,180 at Bonhams, whilst a 4.2kg piece of the Fukang pallasite brought $67,100.
Scored from the planet's surface like angrites and lunar meteorites, Martian meteorites are in terms of collectability and investment the best of both worlds. Since landing a probe on Mars and detecting its composition, we can be certain that certain meteorites have originated from there.
Unlike the moon, the few Martian meteorites which had reached Earth - an amount which in total could be carried in a bag by a person one-handed - are our only source for material from that planet as Neil Armstrong's small step has proved too great a leap to take to the Red Planet so far.
In January 2009, a 9.46g Martian Chassignite (a particularly rare form, thought to have been brought from the planet's mantle) sold for $35,850 - nearly $4,000 per gram!
Overall, this very young market - trading in material which is many millions or even billions of years old - seems set to go from strength to strength as more collectors - such as the director Steven Spielberg - take the hobby up.
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