Materials: Raw: Selenium - Grade 4 - #00019

Selenium is a rare grade 4 element in Elite Dangerous.

Material traders allow trade with almost every other raw 'element' material. If you wish to trade something in for Selenium, you can do so with other grade 4(5) element material with a ratio of 6:1.

Selenium is in Category 4, together with Tin, Zinc and Iron.

It is more favorable to use Tin as a source for a Selenium trade, this class 3 element material has a 6:1 ratio but it's way easier to harvest than grade 4 or 5 material. Just keep in mind if you're planning to engineer your ship with blueprints in need of vast amounts of Zinc, as Zinc is needed for a lot of grade 4 enhancements. Zinc is also often needed for synthesis.

Engineers need Selenium for a broad variety of 'efficient' weapon modifications and various other mods. Mostly used for grade 3 and grade 4 mods, Selenium is something that is needed quite often. Put it on the top of your list when hunting materials.
In addition to modifications, Engineers also use Selenium for effects like the (in)famous Target Lock Breaker. Applied to Plasmas, this effect unlocks your ship as a target on your enemy's gimballed and turreted weapon systems. Several other less important effects should be mentioned.

Synthesis uses Selenium as premium ammo restock for Plasma Accelerators and severl other basic grade ammunitions.

Fortunately, probability of finding Selenium on planets is more than 3 times as high as with other Grade 4/5 Raw materials.

Regular places to find higher quantities of Selenium are best to be searched for by using, three high content systems for example:

No shortcut available

No known geological hotspots like volcanoes