Unity crystals are a race of non-biological life-forms native to P3X-562. The blue quartz crystals emit a low level electromagnetic energy field which has the ability to emulate and recreate other life-forms. When the Goa'uld had come to the planet long ago, they were greeted by the Unity crystals, but when the energy from one of the crystals destroyed one of the Goa'uld, they gathered the Unity into one place and ended it. SG-1 found a pit of thousands of broken crystals and brought samples back to Earth, however, the samples were torn apart by the energy decay caused by Earth's stronger electromagnetic field. The crystals are peaceful, and when O'Neill was accidentally injured by the energy from one of them, it tried to heal him. Not understanding the concept of death, the crystal duplicated O'Neill and his son Charlie, hoping to heal O'Neill's greatest pain, the loss of his son.
Cross Reference: P3X-562
Episode Reference: Cold Lazarus