In Warframe, you will need Hexenon if you want to build some of the new weapons that were introduced in the Jovian Concord update. The Fulmin, Komorex, and Cyanex all require Hexenon to build. You will also need it to build the new Warframe, Wisp.
How To Get Hexenon
Hexenon can be found by killing enemies, opening loot containers, and destroying extractor drones on Jupiter. It can also be earned from playing the Disruption game mode.
The best places to farm Hexenon are the Cameria and Sinai nodes on Jupiter. They have an increased resource drop rate, as they are Dark Sector missions.
Dark Sector missions will also switch the enemy type from Corpus to Infested. These are some of the easiest missions for long farming sessions, due to the lack of Nullifiers, but you still need to watch out Disruptors. Cameria is a Survival mission, so the group farming method will work well here. You can find a spot on the map with one entrance, then stay there and all the Infested will come to you. Running a team with a Nekros will allow you to use his Desecrate ability to re-roll the loot tables of dead enemies, increasing the number of Plastids you will get.
You can also run Warframes like Hydroid with Pilfering Swarm, or Khora with Pilfering Stangledome to increase your loot drops. It is a good idea to have one person bring a stealth Frame so that they can leave the room you use a base and get the life support capsules without dragging away any enemies.
For these missions, it is a good idea to farm for as long as possible. Every five-minute rotation will give you an improved percentage chance buff, and some of these affect resource drops. Plastids also have a good chance of dropping from lockers and containers, so make sure you open everything you find.
If you wish to play Disruption missions, then Hexenon will drop from Amalgam enemies that will spawn throughout the mission.