Ferrite

"Alloy pellets used in Grineer manufacturing."

- In-Game Description

Ferrite is a common component that can be found on Mercury, Earth and Neptune. It is usually found in quantities of 50 to 99.

Gathering Tips
These are based on opinions and may not be true. These should be viewed as advice for finding the materials until better facts are proven.
 * Caloris, Mercury is arguably one of the better places to gather Ferrite -- normally getting between 200 to 1000 a run. Since this level is a low-level exterminate mission with around 50 enemies, you can easily clear the map out, loot the lockers and containers in short order. This allows you to rack up a huge amount of Ferrite quickly.
 * Ferrite can be effectively gathered in large quantities in Neptune, especially on the Mobile Defense Mission Larissa.
 * Thalassa has a large number of storage lockers (although some can't be opened without master thief) . While Larissa is a mobile defense mission, the amount of mobs spawned in it are much lower than that of Sedna's Kappa. Thalassa has a higher concentration of mobs and also contains a high amount of storage containers and lockers, which also have a chance to drop ferrite.
 * Also, Proteus in Neptune has a high drop rate of ferrite. Another endless defense, but this time with infested. There are also tons of containers, and a speed run to wave 5 can yield 200+ ferrite in a matter of minutes.
 * Lua (Mobile Defense) of Earth is good place for farming too, as a combination of Exp and Ferrite.
 * Despina, also on Neptune, is also a very efficient place to farm Ferrite. You are likely to get near 500 ferrite on almost every run.(Confirmed)
 * Tolstoj on Mercury. After you confirm your presence to the enemy, find safe spot, ALT+TAB, go back after 5-10 minutes, kill all, repeat - profit! Alternatively, just clean whole map without waiting. Every third resource drop is ferrite (70-92).
 * Post Update 9, M Prime is still a viable place to farm Ferrite. It will yield anywhere from 400 Ferrite minimum to over 900 a run. Break open all the containers and open all the lockers to achieve maximum possible yield. Master Thief will be of help in achieving as much loot as possible. (Confirmed)