A piece of moon rock is available for sale at a Dutch auction site, with bids starting at USD $50 000. At the time of writing, no-one seems game to put down the money for a 5kg chunk of rock geologically and chemically identical to a $1 piece of Arizonian desert boulder.

Then again, diamond dealers are also so concerned with authenticity as to reject the creation of C_d via any process other than slow geological heating and compression. Both enterprises sound like artificially inflated markets to me (though the lot does include a rather nice gift plaque from the good folks at NASA - there's a bit of a story behind this rock, after all).