A pair of assimilators
assimilator is a protoss building used for harvesting vespene gas. Although materials were usually warped in from Aiur, vespene is still required for these materials to be produced and the creation of warp rifts.
Game Structure Edit
An assimilator must be warped in on top of a vespene geyser before
probes can collect vespene gas from it, packaging the gas for collection. A probe can gather 8 gas in a single run. 
+1 armor bonus to shields per level for all units and structures.
The following section contains information from a previous version of StarCraft beta which is no longer valid.
An early assimilator from the StarCraft beta. A probe can be seen carrying vespene cans away.
StarCraft beta, assimilators possessed a different appearance from their final version.
StarCraft II Edit
Armored, Mechanical, Structure
The assimilator remains much the same as its predecessor in
StarCraft. Probes now gather 4 gas in one run. In addition, the assimilator no longer yields any gas when it is depleted.
+1 armor to shields per level.
Legacy of the Void Edit
, once tier 3 of the StarCraft II: Legacy of the Void solar core is unlocked, assimilators can be upgraded into orbital assimilators for 25 solarite. Orbital assimilators harvest gas automatically.
Co-op Missions Edit
Co-op Missions, Vorazun gains the orbital assimilator upgrade at level 2, allowing her to automatically harvest vespene gas. Zeratul gains access to the ancient assimilator, which autmoatically harvests gas and automatically begins construction when an ancient nexus is built.
Assimilators harvest vespene gas to the without the need for Spear of Adun probes. Passive ability.
Reach Vorazun Level 2
The following section contains information from a previous version of StarCraft II which is no longer valid.
StarCraft II form went through a few revisions before the designers decided upon the current version in-game. The intention for the update was to showcase the functionality a little better by actually seeing the little gas cubes being manufactured inside. The final form is effectively a dome that covers a vespene geyser, with a crater visible inside. 
Heart of the Swarm Notes Edit
Heart of the Swarm beta files mention a terrazine assimilator.
1.0 1.1 Underwood, Peter, Bill Roper, Chris Metzen and Jeffrey Vaughn.
StarCraft (Manual). Irvine, Calif.: Blizzard Entertainment, 1998.
↑ Blizzard Entertainment.
(Blizzard Entertainment) (in English). March 31, 1998 StarCraft.
, accessed on 2011-07-20
SC2: Protoss Assimilator. Deviantart, accessed on 2011-02-15
Assimilator Screenshot Official StarCraft II website. Accessed 2009-01-13. ↑ Blizzard Entertainment.
(Activision Blizzard) (in English). September 4, 2012 Heart of the Swarm beta Map Editor.