Cortosis is a rare mineral from the Star Wars Expanded Universe. It is a somewhat fragile light grey, chalky rock that has the strange property of being impervious to both heat and energy. It is highly resistant to blaster bolts, and cortosis alloys are capable of resisting or even deactivating Lightsabers, the only mineral to do so other than phrik and beskar. The process of mining cortosis requires the use of hydraulic jacks, since its properties render plasma torches useless.
Cortosis is first mentioned in the Timothy Zahn's The Hand of Thrawn duology, and gradually adopted into the EU canon in later works.
In The Hand of Thrawn duology, Cortosis is described as causing a feedback loop with a lightsaber by "shorting out" the blade, requiring it to be reactivated (but not damaging it permanently). In the duology, Luke Skywalker and Mara Jade are in fact able to cut their way through an outcropping of cortosis by hours of repeated lightsaber strokes and reactivations. Later they encounter guard droids with an armor made up of alternating layers of cortosis and blaster-proof armor. Many fans dispute the true nature of cortosis as both definitions have been included in established canon literature. The sources that describe it as "shorting out" the lightsaber blade also describe it as a brittle mineral; bladed weapons used a cortosis alloy to incorporate the mineral's lightsaber-blocking capabilities without its fragility.
In "Darth Bane: Path of Destruction" Darth Bane was born on the world of Apatros, the planet on which Cortosis is mined.
Cortosis is common in weaponry in the Star Wars universe. Many melee weapons are made with a "weave" of cortosis to fight lightsaber bearing enemies. In the ancient times of the Old Republic, during times of war with the Sith, it was common for fighters to carry cortosis-weave vibroblades and vibroswords, which could be used to fight Jedi and Dark Jedi in close-range combat. Sith in ancient times commonly carried a vibrosword rather than a lightsaber for two reasons, firstly, vibroblades would wound opponents in a more painful manner, due to the dicing way the vibroblades cut, secondly, vibriblade wounds are more prone to bleed-out, as the intense heat from lightsabers cauterizes any wound they make.
In the game Jedi Outcast, Galak Fyyar processes cortosis ore into a black armor that is used by his Shadowtroopers. He also builds a suit of power armor that he uses himself. It is unknown whether all cortosis ore deposits are capable of such processing; the ore Fyyar used was smuggled from Cloud City.
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