Etherium

Etherium was a kind of metallic alloy that was infused with magic.

History
Tezzeret's skeletal prosthetic arm was made of etherium and kept charged with mana.

In 150,084 CMT (Day 55 of The Mazkertis Paradox arc), the Kra'lythe Minutún corrupted Cassius Calm's chakra blasts and redirected them into Tezzeret's etherium arm in the Battle of Datrio. The corrupted chakra had a horrific effect on the etherium arm that caused Tezzeret to feel a searing pain. The arm exploded moments later, weakening Tezzeret enough for one of the Kindred of Dawn's mooks to knock him unconscious with a single punch.