Whoa, a big NO on the Shaped Taaffeites. Those are worthless and aren't used for anything, and people selling them in bazaar are 1 of 2 people:
1) Completely unaware that Shaped Taaffeite is useless so they just sell for what others are charging, when really it has nothing to do with jewelcrafting.
2) They are aware it's not used in anything, and are trying to scam people out of some plat hoping to trick them into thinking it's related to the more expensive Taaffeite.
Look for various cuts of Taaffeite:
Round Cut
Square Cut
Marquise Cut
Trilion Cut
Oval Cut
Half-Moon Cut
Pear Cut
Stay away from Shaped Taaffeite!