Crystal key

When the two halvs (The two halves must be different for it to work. Two identical halves will not make the key.) of the key are combined you get the Crystal Key. The Crystal Key is used to open a chest inTaverley. The chest is in the long house North of the Herblore shop.

The Crystal Key can only be used once. When it is used, it dissappears. The chest loot always includes an Uncut dragonstone and will include another random item (your loot could possibly be: just the Stone itself, spinach roll and 2000gp Stone, Runes of varying amounts Stone, Two of each gem(uncut) Stone, 750gp and half of a key stone, 3 runite bars stone, raw swordfish stone, 100 coal stone, etc).

When examined it says: A mysterious key for a mysterious chest.