Petrusite is a powerful element made from a unique form of Higgs Boson molecules only found on the planet Helghan and in a few of its fauna. In Helghan's early years, it was used to supply Vekta and Helghan with energy. By the time of Scolar Visari's reign, Petrusite-made weaponry were developed during the Second Extrasolar War.
Petrusite was accidentally discovered during desert mining operations in the early 2350's when Helghan was undergoing rapid industrialization. The element was first identified by Professor Torr Savic, a leading researcher at the Institute of Science and Technology, who developed a controlled means of using it to generate power. This lead to the development of civil and industrial applications of Arc technology, which include increased automation and the provision of cheap energy to the masses. Petrusite is found in naturally occurring smoker towers and is processed in refineries, using seawater to cool the reactor and refine the Petrusite.
Following the Helghast's failure to conquer Vekta, Petrusite-powered Arc weapons such as the Arc Tower network and VC5 Arc Gun was widely used in the Helghast war machine in defending Helghan from ISA retaliation in Operation Archangel. Private weapons manufacturer Stahl Arms was responsible for developing Arc weapons technology and exploited the rich supply of Petrusite.
Following the aftermath of Operation Archangel, large amounts of Petrusite became contaminated by the radiation generated after Visari destroyed the capital city of Pyrrhus using captured ISA nuclear bombs. Jorhan Stahl, chairman of Stahl Arms, gathered this new and more volatile variant of Petrusite in order to make even more lethal weapons. The latest weapons and systems that are powered by irradiated Petrusite include the StA-5X Arc Cannon, missiles capable of devastating large portions of a planet, and even energy shielding. Ironically, the weaponized Petrusite became the root cause of Helghan's destruction: Jorhan Stahl had a invasion fleet prepared to directly attacking Earth and unleashing payloads of irradiated Petrusite on the planet. However, the invasion was hindered by a civil war between the factions led by Stahl and Orlock, and remnants of the ISA attacking the fleet. The fighting indirectly led to Stahl's Petrusite arsenal unleashed on Helghan, completely destroying the surface of the planet and ending the Helghan Empire. The devastating event became known as the Terracide.
Petrusite comes in a blue natural form. It is highly unstable and if canisters of Petrusite are shot they explode in an electrical explosion and electricity lingers in the area for a brief time.
Irradiated Petrusite is created from being contaminated from the thermonuclear bomb Red Dust that was detonated over Pyrhhus, which had vast quantities of Petrusite underneath the city. It is extremely volatile and can cause organic beings to violently explode. It seems to be violently attracted to any form of nearby movement as depicted in Killzone 3.
The fact that Helghan had a naturally higher amount of radiation than human worlds, coupled with a weaponized irradiated Petrusite explosion was the catalyst for the Terracide.