Garrxax is a small world on the fringes of Terran Dominion space. It has a tropical climate with mountainous rainforests, and high humidity. Heavy rainstorms are common through the planet. Unnaturally warm oceans cover the majority of the planet's surface. The planet's atmosphere is breathable but high nitrogen, and most of the planet's wildlife was either docile or scared of terrans. The planet has an extreme axial tilt which allowed for extremely long periods of daylight in some seasons.
Garrxax is the homeworld of the zantar slug, the evolutionary predecessor to the roach. It has an extremely powerful slime that can eat through neosteel, and powerful regenerative capabilities. Another common lifeform is a vine that has a sap that can attach to neosteel and form a powerful bond, but is extremely flammable sap. When the zantar slug's acidic excretions and this sap combine, the result is an extremely powerful explosion.
The Dominion held a research station on this world to study the native lifeforms there, manned by ten scientists and First Security Officer Lee Treicher (named Illyana Jorres at the time). A wounded zerg behemoth landed on the planet, and attacked the habitation stations in order to obtain biomass. When the zerg found the zantar slugs on the planet, they assimilated it into a new strain, the roach. The base was evacuated, but the instillation was lost to the zerg.
Upon release of the short story "Acid Burns," the planet was misspelled "Garxxax." This was later changed on the version of the short story on the StarCraft II website and the War Stories version, but remains spelled with two "x"es in the PDF download of the story.