Etched Twilight Opal

Several gem patterns have yet to be implemented in-game. All this means is that certain classes and builds have been arbitrarily shafted when it comes to gems.

Where does the pattern for this drop?

Ret paladins that socket Pristine Monarch Topaz instead of this lose 1.6 AP. It's not the end of the world, and as stated above, you're not the only class that prefers Strength to Attack Power.

Your comment is wrong.

Retribution paladins that prefer a Pristine Topaz (+16 AP, +8 Hit rating) over an Etched Topaz (+8 Str, +8 Hit rating) lose 4 Attack Power and not 1.6.

The calculations of course assume that you have divine strength (+15% Str) and BoK (+10% all stats, therefore +10% Str too) which makes the Etched Topaz provide +20 AP and +8 Hit at a raid buffed level.

On the situtation that you are not buffed with BoK but have divine strength, then the difference is still 2.4 Attack Power in favor off the Etched Topaz.

The numbers may seem small, but say for example that you have 5 Pristine Topazes (or whatever the plural of topaz is) equipped on your items. The bonus you get is +80 AP and +40 Hit rating. If you equip 5 Etched Topazes in favour of the Pristine ones, then the bonus you get from 5 is: 100 AP and +40 Hit rating. And so on and so forth.