A distinctly alien species of intelligent, crystalline beings. Cobalt in color, the creatures call themselves "Unity."
When the Goa'uld arrived on their planet, the Unity tried to greet them. After touching a crystal and being thrown across the surface of the yellow planet, the creatures were perceived as a threat. As the remaining crystals tell, the Goa'uld gathered the Unity in one place and used staff weapons to annihilate their entire civilization. Undoubtedly the Goa'uld were unable to take advantage of the species and decided termination of the entire culture was the best possible course of action to prevent a possible future retaliation.
The area around the Stargate is, essentially, a mass graveyard of Unity. At least one crystal has survived to tell the tale.
The Unity crystals are able to copy both physical and auditory characteristics of the person being communicated to, and can move slightly while the transformation process increases. As the crystals lose power, the forms retreat back into the core of the object. If one makes physical contact with a Unity crystal, they are violently blown back across the ground in a concussion wave.
The crystal can automatically clone a full-grown duplicate of the original individual, copying their most powerful memories as well. Though the exact purpose of this is not known, it could be a means the Unity explores the galaxy and learns of that particular species. Unfortunately, humanoids might not be perfectly compatible, hence the concussion wave, absent of knowledge of more recent events (such as the death of Charlie O'Neill), and the eventual degradation of the clone.
Cold Lazarus - SG-1 travels to P3X-562, encountering a mass grave of Unity crystals they later discover to have been living beings.
Doppelganger - Atlantis encounters a similar, crystalline species in the Pegasus Galaxy, when a psychotic energy being invades the team's dreams in the guise of Colonel Sheppard.