Dark iron ore

Dark iron ore is a crafting component in that is needed to craft several items.
It can be found as random loot, guaranteed in a few chests accessible during secondary quests on Ard Skellig, or purchased from the following merchants:
* All armorers and blacksmiths
* Armors and weapons merchants in Nilfgaardian Army Group 'Center' Camp
* Merchant in the boatyard south of Refugees' Camp
* Merchant at Calveit Watchtower
* Merchant at Coast of Wrecks
* Merchant in Ursten
* Merchant by the road west of White Eagle Fort
* Merchant at the sawmill northeast of Rannvaig
* Merchant at the Isolated Hut on Hindarsfjall
* Merchant in Mohrin Village 
* Merchant in Stacheier 
Dark iron ore can also be obtained by dismantling many items, including all witcher gear that is crafted with it. The full list of items is way too long, but the following are all non-crafted items from the base game:
=== Needed to craft ===
Other items:
Witcher gear:
ru:Руда темного железа
Category:The Witcher 3 crafting components