Psitanium is a rare, psychoreactive mineral. Prolonged exposure to it may cause insanity, paranormal hysteria, or even the development of Psychic abilities.
500 years before the events of Psychonauts, a meteorite bearing an enormous amount of Psitanium crashed to earth. Much later, the natives of the area started making arrowheads out of the material, calling it "whispering rock" (rough translation).
When settlers founded a town called Shaky Claim in the area, many soon lapsed into madness, leading Houston Thorney to build an asylum to house the victims of the hysteria. The asylum finally closed when the government evicted the last residents of Shaky Claim, flooding the area into what is now Lake Oblongata.
Many years later, Whispering Rock Psychic Summer Camp was created in the vicinity of the lake. Deposits of Psitanium arrowheads buried by the natives are used as currency there. It is also the home of the largest Psitanium deposit in the world, located in Ford's Sanctuary.
In Rhombus of Ruin it is revealed that Psitanium has a negative counterpart, Psilirium. Psilirium has the ability to greatly inhibit psychic powers and make psychics hallucinate and become deliirious.
- Psitanium is the only thing keeping Ford Cruller's shattered psyche together, when not near it, he lapses into one of his alternate personalities. Ford had to carry a Psitanium backpack when he went out of the Sanctuary to stop him from changing into an alternate personality in the cutscene at the end of the game.