"Psitanium is a very rare, psychoreactive mineral that crashed here on a meteorite hundreds of years ago. It responds to psychic waves. Focuses them, amplifies them. It can make psychics more psychic, but it can also make unstable people more unstable. Not everyone can handle that much activity in that part of their brain. It can drive them completely out of their gourd. Gives this valley an interesting history." — Ford Cruller, explaining Psitanium to Raz
Psitanium is a psychoreactive mineral, stated to be rarely-occurring and found in meteorites, and possibly of exclusively extraterrestrial origin. Prolonged exposure to it can cause insanity, paranormal hysteria, or even the development and strengthening of psychic abilities.
As a psychoreactive substance, psitanium responds to psychic waves, focusing and amplifying them. These properties can allow for further development of psychic abilities in those gifted with them or who had the untapped potential to use them, and can even unlock psychic abilities in those previously not known to have them whatsoever. However, prolonged exposure to psitanium can cause insanity and paranormal hysteria in non-psychics, as many cannot "handle that much activity in that part of their brain", as Ford explains it. Those who already mentally unwell seem to have a higher chance of developing psychic powers than others, but their mental state leaves them incapable of using them correctly.
Psitanium also has mutagenic properties, and the psitanium residue in the food chain in the area of Lake Oblongata has caused psychic mutations in the local wildlife, resulting in animals growing larger than average, gaining psychic abilities, or developing intelligence equal to or possibly greater than that of a human being. Pyrokinetic cougars, telekinetic bears, hyper-intelligent squirrels, brainsucking suckerfish, giant crayfish, confusion-inducing explosive rats, telepathic lungfish with psychic shields, and a sapient talking turtle capable of psi-blasts are just few examples of Psitanium-induced mutants.
According to the log timeline, 500 years before the events of Psychonauts, a meteorite bearing an enormous amount of psitanium crashed to earth, creating (what is stated to be) the largest known psitanium deposit in the world. Much later, the indigenous people of the area made arrowheads out of the material, calling it what is roughly translated as "whispering rock". When settlers drove away the indigenous residents and founded the town of Shaky Claim in the area, many were driven to madness by the effects of the psitanium, leading Houston Thorney to build an asylum to house the victims, before becoming a victim of its effects himself. The asylum (reportedly) closed when the government evicted the last residents of Shaky Claim, flooding the area to create what is now Lake Oblongata. Many years later, Whispering Rock Psychic Summer Camp was created in the vicinity of the lake by the Psychonauts, and the psitanium arrowheads left by the previous indigenous residents of the area became used as currency at the camp store and between campers. Ford's Sanctuary is located directly above the psitanium deposit.
It is implied that Whispering Rock is not the only place where psitanium can be found, due to its status as the "largest known" psitanium deposit in the world, as well as the description of the dinosaur bone suggesting the existence of "levitating velociraptors", with velociraptor fossils having been specifically found in what is now Mongolia. The existence of other psitanium deposits is further confirmed in Psychonauts 2, as the Psychonauts HQ is built in the remains of a psitanium quarry.
In Rhombus of Ruin it is revealed that psitanium has a "negative" counterpart, Psilirium, which has the ability to greatly inhibit psychic powers and cause delirium and hallucinations in psychics, not unlike the effects psitanium causes in non-psychics.
- Psitanium is the only known way for Ford Cruller to remain stable as his true personality, due to his shattered psyche causing him to lapse into one of his alternate personalities if not directly next to it. Ford initially claims this means he is unable to directly be involved in stopping Oleander, as once he leaves his sanctuary his alternate personalities will not remember this goal or what to do in response to it, but at the end of the game rigs up a Psitanium-filled backpack to remain cognizant of himself outside of his sanctuary, and joins forces with Sasha and Milla against Coach Oleander. The Psitanium in his backpack becomes seemingly drained of power in the game's ending cutscene, causing him to lapse back into one of his alternate personalities.