A psicrystal is a fragment of a psionic character’s personality, brought into physical form and a semblance of life (via the Psicrystal Affinity feat). A psicrystal appears as a crystalline construct about the size of a human hand.
Because it is an extension of its creator’s personality, a character’s psicrystal is in some ways a part of him. That’s why, for example, a psionic character can manifest a personal range power on his psicrystal even though normally he can manifest such a power only on himself.