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If you're just looking to farm for skill increase in jewelcrafting, you're much better off simply farming any money place, and buying the gems off of any gem vendor. In the case of silver, electrum and gold, work your way up to emerald (and either re-sell back to vendor for near-cost price, or enchant and sell in the bazaar), and don't even bother with the higher level, more expensive gems.

As a level 42 BST, a good place to hunt might be the Feerrott, outside CT -- lizards drop decent plat and FS weapons, and some will still give you exp. Once you get into the mid-higher 40s you can go to the geos camp in Crystal Caverns, which has gotten me ~9K tops so far in a night.

Hope this helps. :)