Created using the alloy known as durgolium. Chests or boxes made in this way are often used to protect and hide objects from other planes. Some may look quite plain. Others will bear markings or carvings.

Entering the outpost near Blacklake, you discover a durgolium chest guarded by the Ogre Tog;

Between his angry cries, he smashes the metal chest with such force that it shakes the ground around you. But the chest only rings out a remarkably pleasant tone. It remains unbroken, undented, and firmly in place. - Battle at Blacklake (RPA-ADV1)

Upon opening the chest, Tarik gives you a sack made of the same metal to extract and house the prize within. Within the chest is a jar of Gray Matter.

Upon solving the puzzle in the Chamber of Illusions, you open the durgolium chest. Inside, you find the imprint of a jar and a brooch, clearly both items of value to someone.

You open the durgolium box, but the earth does not shake. No energy crackles over your head. - Eye of Ulos (RPA-ADV4)

You discover the Immortal Knight's Helm in one durgolium chest. It may be used to return you to Ulos.

Among the many items you find in the crystalline frog's mouth is a chest made of durgolium. You last saw it in the possession of Zug's body as he was cast into the fissure at Dunshab Lakebed. This one has intricate carvings of a dragon on its lid.

Retrieving it is not an easy task. As you open it, crackling energy swirls overhead. Inside you find a tiny crystalline tadpole. You have awakened it so you quickly close the box, calming both the air around you and the tiny creature inside.

Queen Gimnax is quite interested in this box, if you are able to retrieve and deliver it to her.

If you are carrying the box that was in Zug's possesion, Alpha-Zero will ask to open it. Inside, the small, crystalline tadpole is awake and wriggling around. Alpha-Zero will place the tadpole in her chest cavity, causing a surge of blue energy.