I've been in Stormdrain Tower recently and I see an obsidian chest. I remember seeing one in my first Nirini dungeon after defeating the boss (I forgot the name).
But this question occurred to me. Could anyone answer this?
As Seethe stated, you will need to go back to them for a quest later in the game. I don't think it will be the last you see, as there're about 7 chests.
For a Dragonspyre quest, in Dragonspyre Academy in which you talk to Ashley the Fire Tree. In each of the chests is a piece of Dragon Rider Staff, to control a Battledrake to fly to Malistaire's Chamber. Chests are located in specific places, so it won't be easy to just find one. All chests are guarded by enemies you have faced before, so the battles are not really challenging.
