Medieval alchemists once dreamed of finding a process to turn lead into gold. Had they been successful, we would not now be looking to Fort Knox for the yellow metal, but rather to the local hardware store.
Value lies in either utility or scarcity.
Other than diamond dust for grinding purposes and rubies for lasers, it is difficult to find much utility in pretty rocks. Scarcity is the key. Sophisticated analytical instrumentation is often all that stands between the public and the chemist's new artistry of gemstone creation and enhancement. Spectroscopy often provides the only means for separating the fake from the fabulous. And as gemstone technology becomes increasingly advanced, the tools for detecting its art must also become increasingly sophisticated.