These bags only hold ingredients for Jewelcrafting, but are larger than the average general bag. Only 1 gem bag may fill a slot in a bank at any time.
“ Gem bags are special bags that can store minerals and gems. The [Gem Pouch] is a 20-slot gem...Gem bag
“ Luxurious Silk Gem BagItem Level 85Disenchants into: Not disenchantableBinds when equipped36...Luxurious Silk Gem Bag