I do '50gp onyx & 2x 75gp opals' over "3x gems totaling 200gp" because my games tend to allow for crafting. Red gems for fire items, blue water, tiger eye for vision/animal items, etc. I also give the "sale" price of gems by default so they can properly value them as a currency. Between people of a certain economic tier, a handful of gems is far easier to manage over chests of coins.
I do make low level (tier 1) characters make skill checks to appraise but by tier 2 they should be pretty good at guessing the values. Of course, I also think casters are a key driver of gem values (at least pearls, rubies, diamonds) so "appraisal" is often "how many of these rubies would be required to cast Forbiddance?"