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 bag...Gem bag
“Bag of JewelsItem Level 65Disenchants into:Not disenchantableBinds when equipped24 Slot...Bag of Jewels
“Luxurious Silk Gem BagItem Level 85Disenchants into:Not disenchantableBinds when equipped36 Slot...Luxurious Silk Gem Bag