Treasure Coffer

From FFXIclopedia, the free Final Fantasy XI encyclopedia

These are coffers containing different treasures that are found in some dungeons throughout Vana'diel. Coffers are typically in higher level areas and have better contents than Treasure Chests. In order to open a coffer, you either need the appropriate key, or need to be a Thief (Main Job) with a lock-picking tool. The keys to open the coffers are dropped from specific mobs, which are usually located in the same zone as the coffer.

When you open a coffer you will either randomly get one of the possible items, some gil, or a quest item if you have a pertaining quest active.

Please note, that while you are weakened, you cannot open a Treasure Coffer. Coffers cannot be opened while invisible, and opening a coffer will result in losing effects of Sneak and Deodorize, possibly in aggro from surrounding monsters, so special caution should be used when opening one.

Coffer respawn time seems to vary between 15-30 minutes

See also:

Treasure Chest/Coffer Guide for information on specific coffers

Picking your Coffers and Chests for Thief specific informaion