Titanium Ore is the rarest and most valuable of ores. It is used to make Titanium Bars.
It takes three chops of a Gold Pickaxe to mine 1 ore.
Titanium can be found on Titan's Tremor (3-15), Ceres's Core (3-07), Caress of Callisto (3-12) and Io's Interior (3-06). The NPC Uco the Miner on Caress of Callisto has a non restocking limited supply of Titanium Ore. It also drops from all Hard Mode bosses as well as Normal Mode Ghost King. Other ways to find some include special events where it is a typical chest drop and coffins from the C'Thiris Tesseract special island.