Magnetite

Magnetite is a magnetic Raw Material that can be found in the Mountains biome and inside the caves there. Due to new build updates near the end of 2015, this raw material can no longer be found inside the snake mushrooms in the Jelly Shroom Caves. The Magnetite appears as a reddish brown stone with bright blue spots that are vaguely bioluminescent.

Magnetite was scheduled to be moved out of the snake mushrooms in the following reference.