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Shards of a reactive metal that stores whatever energy it is exposed to.
― In-game description

A Hadium Flake is a material introduced in The Taken King. Hadium Flakes can be used to purchase Moldering Shards from Eris Morn, unlock upgrades on Touch of Malice, or obtain a sword during the quest A Broken Will. They can be obtained randomly from loot chests on the Dreadnaught.