Psijic Portals contain items based on the location you find them in. This includes:
...
An Aspect, Essence, and Potency Rune.
The Aspect Rune is never a Ta (white) rune. It is always at least green-quality, and may be up to gold-quality.
The Essence rune may be any Essence rune currently in the game, including, rarely, a Prismatic rune.
The Potency rune is based on your Level or Passive rank, in a 50/50 split.