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.
The Heart of the Ocean didn't really exist, it was based on the real life Hope Diamond, estimated to be worth approximately $250 million.
The dream is worth 400 million
Any diamond is worth whatever someone will pay you for it.
Any diamond is worth whatever someone will pay you for it.
Anything!!
100-10000 USD
Any diamond is worth whatever someone will pay you for it. Z4 is not a common notation that describes a gem-quality diamond.
I think you are asking if a natural clean diamond is worth as much as a natural diamond that is Not considered clean? The answer is no. A clean diamond means that it is clear from imperfections. Now this can mean clear to the naked eye, or clear under a microscope. Of course the diamond that is clear under the microscope is much worth more than a diamond that is only clear to the naked eye.
It depends on the cut and the grade of the Diamond.
Your answer depends on the quality of the diamond you're buying/ selling.
£2
$300m ish