"Any guesses what it's used for?"
"Well it would definitely affect brain chemistry, so it could be used as some kind of a drug or stimulant I suppose."
Terrazine gas is a potent psionic reagent. It is sought by protoss, zerg and terrans alike. The protoss consider it "the Breath of Creation" (literally translates as such via Khalani). The Tal'darim believe that terrazine is a gift from the xel'naga to allow communication with them.
The properties of terrazine appear to be foreign to the material universe—it has been speculated that terrazine's origins lie within the Void, as on Slayn, it was found in the presence (or emitted) large amounts of Void energy. The presence of terrazine in large amounts can sustain Void shades, albeit not at full strength. The Tal'darim used terrazine to become closer to Amon and to "peer beyond the veil."
Terrazine is similar to vespene gas, and contains additional organic substances, though is not as flammable. Without special preparation and containers, samples don't last long. Visually, terrazine has appeared to be purple and misty green. Terrazine can be extracted from some creatures, including the Jarban glider.
Terrazine has a coppery, blood-like smell.
Biological and Psychological
Terrazine's effects are unpredictable, though it possesses mind-altering qualities and can enhance the psionic power of ghosts and other psychics, increasing their power by 1 or more points on the Psi Index scale, though the effects would probably not be noticable on an individual possessing an average PI. Gabriel Tosh believed this could increase a ghost's powers to near those of the protoss. Terrazine also rejuvenates a terran's brain cells, allowing them to overcome memory wipes and other such treatments. At least some spectres can also more easily resist mind-reading and can avoid picking up unwanted thoughts.
Terrazine's side effects include hallucinations and violent outbursts. The exact effects vary somewhat from one individual to another. Many spectres became eccentric, collecting devices such as dolls in an effort to enhance their powers. However, if given in microdoses many of the side effects can be mitigated.
Nova Terra claimed that terrazine drove the users insane, and the instability resulted in the shutdown of Project Shadowblade. Tosh and an independent researcher, Dr. Ariel Hanson, said that Terra had exaggerated its effects.
Terrazine has a half-life of several hours, but it builds up in the system over time and with repeated use. It is addictive, causing withdrawal symptoms after several hours. Stabilized by a little jorium, terrazine is inhaled by spectres like a drug. If the spectre keeps to a strict schedule, the side effects are minimized.
Enough exposure to terrazine can change a terran's eye color to violet. Individuals affected by terrazine that came under Amon's control displayed increased speed and aggression. Increased adrenaline within his forces triggered unpredictable transformations, sometimes at the point of death. Some of his hybrid would even detonate akin to a nuclear weapon upon death.
After terrazine exposure, some viruses can become more lethal.
Terrazine is a substance with a composition foreign to our universe, and was likely brought from the void by Amon. It has been used by the Tal'darim for millennia, as a holy object they believed brought them closer to the xel'naga. They continuously seek out planets rich in terrazine and convert them into shrine worlds. Terrazine has proven catastrophic to native life though, as shown by the destruction of the jungles of Slayn.
Terrazine was first discovered by terrans on Demon's Fair by an unmanned probe in 2501, in a set of Tal'darim ruins. After its ability to generate psionics in terrans was discovered, Project Shadowblade was commissioned for the creation of spectres, with General Horace Warfield being put in charge of the project. However, the miners and test subjects began to experience erratic behavior, within a year the project was shut down. Everyone involved in the project was either killed or sent to a correctional facility, with the exception of General Warfield, who retired, and Cole Bennett, who survived and infiltrated Nova Squadron under the alias of Jackson Hauler.
Elements of Project Shadowblade survived however, and renegade ghost Gabriel Tosh discovered the substance from a man whose brother was in the program. Tosh met with Cole Bennett, and the two rallied his former comrades from Ghost Academy, and discovered a rift of the substance on Altara. Using the terrazine, the ghosts began to regain their former memories, and grow in power, plotting revenge against Emperor Arcturus Mengsk and his corrupt Terran Dominion. They lured ghosts to the world to indoctrinate them, and soon detonated the refinery for the gas to draw the attention of the Dominion.
The explosion drew the zerg to the planet en masse, and the Dominion engaged the zerg, forcing them back. However, Nova and several other ghosts were exposed to the terrazine, triggering a recovery of memories. The spectres soon struck Augustgrad in an attempt to capture Arcturus Mengsk and force him to admit his crimes. While they were unsuccessful, they were able to force Agent Nova Terra to inhale more terrazine, further forcing her memories back. Arcturus Mengsk explained the history of terrazine to her and Wrangler Malcolm Kelerchian the history of terrazine and the spectre project.
The spectres then struck at Korhal, slipping into Korhal Palace with the intent of capturing Mengsk and forcing him to confess his crimes to the public. Agent Nova Terra and the Annihilators lead a defense of the palace, but in spite of being outnumbered the spectres put by a brutal fight. The spectres were unsuccessful in capturing Mengsk, but killed ninety-seven Annihilators, and all but two of Nova's ghost agents, both of whom were captured and exposed to terrazine. Nova herself was exposed to terrazine during the fight, a fact with Major Spaulding took major issue with. Mengsk himself then took Nova and Kelerchian aside and told him the full story behind terrazine and Project Shadowblade.
However, wishing to bring Nova into their ranks, Bennett played his hand, and gassed Nova and Kelerchian as they investigated the nature of the spectres and where they were operating from. He took them to near Gehenna Station, where the spectres operated. Nova escaped the Palatine, and slipped aboard the station, discovering that tanks of terrazine were being used to convert ghosts into spectres. Nova killed Bennett, freed Kelerchian and escaped the station, which was destroyed by a nuclear missile launched by Major Spaulding. With that, the spectre rebellion had been halted. However, Gabriel Tosh had escaped aboard the Palatine with six psionic waveform indoctrinators, and swore he would restart the program.
The Second Great War
During the Second Great War, Gabriel Tosh commissioned Raynor's Raiders to steal terrazine from protoss altars on Bel'Shir. The altars were guarded by the Tal'darim, who regarded the gas as a sacred gift from the xel'naga, and refused to give the terrans any. The Raiders took what they needed by force.
Tosh intended to use the terrazine to create an army of spectres. He stored his terrazine in a terrazine tank on Avernus Station. Raynor was contacted by Nova as they attempted to free the spectres from New Folsom, and she informed him the effects the gas had on terrans.
Unwilling to unleash an army of psychotic killers on the universe, Jim Raynor allied with Nova against Tosh. Nova infiltrated Avernus Station, and destroyed the terrazine tanks, along with the jorium stockpile and psi indoctrinator needed to make spectres. Afterward, she killed Tosh, once again stemming the threat of terrazine enhanced terrans.
Though Raynor was concerned about Tosh not telling him the full extent of his operation, Raynor trusted him more then Nova, and proceeded with the operation to break into New Folsam. Tosh personally disabled their defenses, freeing the spectres trapped within. The terrazine enhanced terrans fought alongside Raynor's Raiders, and Tosh ensured that they would be under a strict training program to minimize the side effects of the terrazine. They aided Raynor even through the late staged of the Second Great War, and maintained loyalty to him even after his capture at the hands of Mengsk.
The End War
During the End War, the Tal'darim Alarak sought out Hierarch Artanis for aid in challenging Highlord Ma'lash, so he might claim his title and cease hostilities with the Daelaam. Upon arriving at the Tal'drim homeworld of Slayn, Alarak tasked the Daelaam to target Ma'lash's four lieutenants on the surface. During the battle, terrazine would rise from the underground, in which Amon's forces would emerge and attack until the mist subsided. After successfully killing Ma'lash's lieutenants, Alarak breathed in the terrazine and was pleased to feel Amon's fury at his defiance.
The return of Amon also impacted the terrans exposed to terrazine, who began to fall under his control en masse. Spectres made up a large number of the forces of Moebius Corps, and participated in the assault on Korhal, the raid on Ulnar, and the final defense of the main Moebius Corps base of Revanscar. However, not all spectres fell under the control of Amon, and groups were present with the forces of Jim Raynor during the final attack into the Void.
Defenders of Man Insurgency
Terrazine continued to be sought after years later. The Umojan Protectorate sent an expedition to Jarban Minor, and began to extract the substance from the local Jarban gliders. However, they were attacked by the zerg and overwhelmed, and many were infested in the process. Later, Highlord Alarak guided Nova Terra to the planet as part of a bargain. Nova fought the zerg, the infested Umojans and the forces of First Ascendant Ji'nara in order to harvest the terrazine. She was successful, and used the terrazine to undo the mind wipe she underwent from the Defenders of Man.
This article or section contains information about StarCraft: Ghost, which has been declared non-canon. Elements may be taken as 'flavor lore' however.
Mar Sara featured a Dominion-operated "Vespene" Refinery BF 1138, a terrazine refinery on Mar Sara, disguised as a vespene refinery, which was infested by zerg and had to be rescued by Nova (a ghost) and other Dominion forces.