The Quicksilver Sea is large body of liquid metal on Mirrodin. Though the sea resembles mercury, it is actually an otherwordly liquid. Islands of solid metal, probably tin, arise from the sea in strange formations. The vedalken live in a massive structure called Lumengrid, located somewhere near the shore of the Quicksilver Sea, while their Neurok servants dwell in settlements of tin on the shore nearby. The Blue Lacuna, located beneath the Pool of Knowledge, was in the general area of the Quicksilver Sea.
In the Quicksilver Sea was a spot where the liquid simply refused to flow - a large, circular space where the "floor" was the silvery sea bed and the "wall" around the space was quicksilver suspended as though by a forcefield. Within this spot stood the Titan Forge, a huge device for creating towering metal colossus after colossus.
With the Phyrexianisation of Mirrodin, the waters of the Quicksilver Sea have been modified. Glistening oil has been mixed with the liquid metal, creating a fluid that quickly corrodes away living organisms and artifacts, their spare parts later used for the creation of new things. In spite of this, members of the Progress Machine have built an "underwater" laboratory that is designing sea monsters.