Crystal Key

Let us begin with a small introduction to the world of crystal keys, Crystal key was originally placed in the game late December, 2012. From this they introduced all sorts of misc items, such as the god set of Mitre hats, such as the Guthix, Zamorak, Saradomin and of course the Ancient Mitre. they also introduced the first Dragon hide sets that included the gods, such as Saradomin, Zamorak and Guthix D'hide.

Formation of the C'key.
To form a Crystal Key or C'Key for short, you're required to obtain the Loop half Key and the Tooth half key, these two items can be obtained from any Zamorak foe,  the rarety depends on the drop tables of the specific creature, however you've got greater chance weilding a Ring of wealth purchased from Vote points.

Using the key.
To use the fully formed Crystal key, you'll need to head to the home of Zamorak, and directly behind the bank there will be a dark green chest, standing there a few feet besides the altar, there you'll be able to click on the chest, please note you won't be able to recieve your loot if you click directly on the chest, you'll need to use your key on the chest, failing to use the key on the chest you'll receieve a message that looks more along the lines like this.