I never noticed any more demand (and hence higher cost) for any of the individual gems obtained from mining other than the ecru citrine, which people need a lot more of for the enhance pots rings. I tend to use emerald, ruby, and diamond more because I make arcance circles for deco, but all the gems on vendors I have ever seen always cost the same, except the citrine.
The white pearls are a completely different resource, as they require fishing skill. They used to sell for around 50K each, not sure now. I know the quiver you can make with them is completely worthless considering the material costs, but there are a couple of other recipes that need the pearls.
I'd probably find a good use for the pearls in deco, as I have with the other gems I have mined up myself, but I never was willing to pay 50K each for the privilege of having a white ball, and I lost interest in fishing long before RoT. The seas of Sosaria are teh boring.
And in case you ask...brilliant amber is obtained via lumberjacking at very low drop rates for humans I might add. The bracelet you can make with tinkering skill using a lot of this scarce resource is almost good enough to put in the nearest trash can, but not quite worth the effort to walk to one. I never made anything else with them, not sure what else calls for the brilliant amber. Seems like it used to sell for around 5K each but don't know if anyone actually bothers to buy or sell it now.
-Skylark