This might be the least known of the most expensive gemstones, but that doesn’t mean you shouldn’t add one to your collection, if you can locate one. Perhaps the reason it is not well-known is because it is so rare. You can only find this stone in Tanzania and Sri Lanka. Thus, due to their rarity and beauty, some taaffeites have been valued as high as $35,000 per carat. If you’re lucky enough to find one it makes a great collection piece.