Manabane

One of the more interesting ores in my world is named manabane. Known about by the human continent for less than a hundred years it isn't commonly used yet. When it is, the ore is typically smelted into the swords, arrowtips, etc. Manabane weapons have a very distinct swirling pattern and appear to glow a bit. When manabane comes into contact with the bloodstream it makes channeling mana into magic excruciatingly difficult. Manabane shackles are used on prisoners in a few places. Relatively new, they involve manabane stakes driven through the wrists and held in my place by a metal bands. They are the most reliable known way to keep magic users under control but are obviously cruel. That being said, a few very powerful (and very unpredictable) imprisoned mages do wear them as mages are notoriously difficult to contain.