Tainted is one of the many crystals on this mod. Tainted crystal is a dark purplish color and produces small black puffs of smoke. It is the rarest kind of crystal. Learn more at Vis.
Additionally, a tainted crystal can be created by allowing any other type of crystal to become Tainted due to spreading Taint. Tainted Vis Ore grows best in areas with high levels of taint. Having tained crystal in an area is beleived to increase taint levels as well. Reasearching tainted vis crystal has a chance to give you a concentraited taint theory. Using the concentraited taint will turn an area into a tainted area theoreticly.