Kirine is an rare precious mineral that has an unique mana resistance properties. When there was no mana inside the kirine, mana resistance is zero which allows all mana to pass through it without any effort. The property of it changed however when mana was placed inside the threshold. It would be extremely resistant to outside mana making it almost impossible for foreign mana to enter inside the mineral. Mana that was stored inside could still move in and out of the mineral without any problem.
Kirine's mana resistance made it very useful for protecting enchantments from attempts of breaking them. If an enchantment was placed on it and mana was reached inside, no one could damage the enchantment without breaking the mineral. Enchanters could use a strengthening spell that make it more difficult to break the mineral. Kirine is so rare that it was able to be crafted into weapons and armors. Even a small pearl of kirine cost an incredible fortune.