How much is the ocean dream diamond worth?

The Ocean Dream owned by Cora Diamond Corporation, is currently visible in the Smithsonian's exhibit of diamonds (below).

This more than five carat stone is exceedingly rare, given its natural blue-green colour. Blue diamonds of this size sell for multi-millions of dollars (US), so this one would probably be more expensive.

Added 11/1/2010

This diamond is priceless. The value is only limited by the limit of the deep pockets of the buyer. It is a unique, one-of-a-kind diamond, thus really impossible to put any price on it.

Other diamonds that are rare and available to buy: someone could put a price on it. Fancy color diamonds of half a carat to two carats are known to fetch hundreds of thousands to millions of dollars. Until it's purchased -- usually at auction, it is impossible to put a price in such a diamond.