Big diamonds are hard find. So are colorless, transparent, and flawless ones. Therefore, they are high in price. It is understandable; however, it does not necessarily mean that those diamonds have high value. Prices only talk about diamonds as commodity, and values are different thing.
People who buy the commodity decide the value, and not by the one who sell. There are certain conditions which would change purpose, meaning, and reason to buy a diamond. That is the value.
One most important value of the diamond is its beauty. Everyone appreciates its beauty. However, it is very questionable that many people were successful to buy the most beautiful diamonds. The most important value to buy diamonds has to be its beauty, for both people who buy and sell diamonds. Beauty is the true value of diamonds.