You can sell jewelry for the same price as the equivalent weight in whatever purity of precious metals it is and I specified same weight in the parent comment. They won't be the same price originally, but that's not particularly germane to this discussion of whether there should be a sales tax on one vs the other.

And for what it's worth, people buy things for different reasons. It's very common for Indians to explicitly value jewelry as a wealth store (among other reasons), to give one example.