You should collect all seven Mysterious Ores and keep going – do not sell or discard them. Once you have all of them, they automatically combine into a quest item called Arkhium Stock, which you then use in a special mechanism in Fontaine to unlock puzzles, a secret room, and high‑value rewards.

What the Mysterious Ore is for

  • The Mysterious Ores are part of a hidden “collect them all” objective in Fontaine, not normal forging ore.
  • When you gather all seven, they auto‑merge in your inventory into Arkhium Stock , a unique quest item.
  • Arkhium Stock is then used in the Forging Press / production mechanism in the depths of Fontaine (near the Fortress of Meropide / Millennial Pearl Seahorse areas, depending on the route you follow).

In short: they’re the key ingredient for a one‑off, late‑game Fontaine puzzle and secret area.

What to actually do with them

Once you’ve picked up your first few Mysterious Ores, just hang on to them; the game won’t fully explain their purpose until you have all of them.

  1. Collect all seven Mysterious Ores
    • Some come from world quests like Road to the Singularity, Treacherous Light of the Depths, and the Unfinished Comedy chain (An Eye for an Eye sub‑quest).
 * Others are found by **exploring Fontaine’s underground / workshop areas** , like Central Laboratory Ruins, the Experimental Field Generator surroundings, and underwater rock piles you break with a Xenochromatic Jellyfish.
  1. Let them combine into Arkhium Stock
    • When you’ve got all seven in your bag, they automatically fuse into Arkhium Stock (you don’t need to craft anything manually).
  1. Use Arkhium Stock at the Forging Press / mechanism
    • Take Arkhium Stock to the underground forging mechanism in the abandoned production/press area tied to Fontaine’s endgame exploration.
 * Using it there lets you generate **Arkhium Lumenite** , which is the processed form you need. Expect a small timing/puzzle sequence while operating the press.
  1. Open the secret room and grab rewards
    • With Arkhium Lumenite, you can unlock a sealed door / secret treasure or study near the Experimental Field Generator / hidden study area.
 * Inside you’ll find things like:
   * Luxurious chests
   * A Hydroculus
   * Extra loot and lore tied to Fontaine’s research.

If you’re wondering “Can I just ignore it?”

You can leave the ores sitting in your inventory, but you’ll miss out on:

  • A Luxurious Chest (or more than one in some routes).
  • A Hydroculus needed for maxing out the Statue / progression.
  • Extra background story on Fontaine’s experiments and facilities via the hidden study/treasure room.

Since this is a one‑time, exploration‑style secret, it’s worth finishing once you’re already questing around Fontaine.

Mini FAQ

Do I need to use the ores at a blacksmith?
No. They never go into normal crafting or weapon forging; they’re only for this special mechanism and puzzle.

What if I only have 1–2 Mysterious Ores right now?
That’s fine; just keep playing Fontaine quests like Road to the Singularity , Treacherous Light of the Depths , and Unfinished Comedy , and explore Fontaine’s underground ruins to find the rest.

Can I mess this up or “waste” the Arkhium Stock?
No permanent miss: it’s a guided puzzle once you reach the press area. Follow the prompts and you’ll end up with Arkhium Lumenite and the door unlocked.

Information gathered from public forums or data available on the internet and portrayed here.