Obsidian Treasure Chests can be found on the Stalactite layer underground and deeper caves that will lead into this layer, where they will spawn randomly at any time of (ingame-)days as soon as player-characters come into range of view (no direct line of sight needed though) on Stalactite or Limestone, more rarely on Nodes or other natural blocks. It's hard to make them spawn in artificial biomes.
All Treasure Chests can only spawn on solid natural blocks in darkness, but will stay where they are when you place torches next to them or when the sun rises after they have already appeared. You cannot put anything inside these special chests, and if you take "everything", you will not receive any chests or the like, but only the contents of the chest.
Treasure Chests will vanish if all player-characters wander off too far. Half-looted chests will prevail a little longer so you can teleport home and return within a short while, but will disappear if you do not return for a longer time or if all player-characters log out.
Obsidian Treasure Chests can - randomly - contain (as of R26 in December 2015):
- Notes and/or Data Chips
- Perfumes (Eau De Pigsy, Fantasia De Leafi, Arome Chizzard, L’Rockster)
- Pet Accessoires like Hats or Bows
- Basic Extractors
- Coal Torches
- Stone Swords
- Stun Bombs
- Explosive Bombs
- pieces of Leather armor
- Stacked Stone Walls
- Arctek Chests
- Red Wood Walls
- Brown Mushrooms
- rare recipes like colored Bed or Stone-based building blocks