Unity is a race of blue crystalline lifeforms found on P3X-562.
When the Goa'uld Kur visited their planet long ago, Unity tried to greet him. Kur touched one of the crystals and was killed. In retaliation, the Jaffa gathered Unity in one place and attempted to destroy them with staff weapons. Only a few crystals survived, almost none of them whole.
In 1997, SG-1 visited P3X-562. While there, Jack O'Neill touched an intact crystal which rendered him unconscious. In fear of another retaliation, the crystal took O'Neill's form in hopes of fixing his pain. However the greatest pain it found in O'Neill wasn't physical, but emotional; the death of his son Charlie. Not understanding what death meant, the crystal Jack went to Earth looking for Charlie to bring him back to O'Neill. Samantha Carter brought some of the crystals back to Earth for study, however one of the crystals made contact with them, telling them Unity's history. Through further study, Carter found that the crystals couldn't survive in the Earth's stronger electromagnetic field and released radiation as a result. The crystals along with crystal Jack, then in the form of Charlie, were returned to the planet.(SG1: "Cold Lazarus")
In 2007, when encountering the Crystal of M3X-387, Carter explains the Unity incident to Lt. Colonel John Sheppard, Teyla Emmagan and Doctors Kate Heightmeyer and Jennifer Keller as an example of how an alien entity could exist in a crystalline form. (SGA: "Doppleganger")
The Unity are unlike other races that inhabit the Milky Way galaxy as they are not organic but actually a crystalline species. They are essentially energy beings that inhabit crystal containers. They derive nourishment from a planet's electromagnetic field, however, they can only survive in a set environment like their homeworld and planets, such as Earth, possess too strong a field which can result in them losing control of their abilities.
Though they appear as crystals, the Unity are capable of manipulating electromagnetic fields and energy to a fine degree. This allows them to reshape their bodies into near perfect imitations of other lifeforms. They are also capable of gaining the memories of those that touch them. In addition to this, they are capable of projecting this energy from their body into destructive bolts.
Though a peaceful species, many of the Unity became divided on their encounter with the Goa'uld. Some, such as the Unity Pacifists, blamed themselves for the encounter while others, such as the Unity Vengeance Seekers, took an active part on attacking the Goa'uld. (RPG: "Fantastic Frontiers: Stargate Season One")