Force Metals, when refined, typically take the shape of a small hexagon that reploids insert into their armor.

In 21XX (2170) a large meteor fell into the Pacific ocean. A team of researchers went looking to figure out what it was and if it held any useful properties. What they discovered though was beyond their dreams…

After recovering a sample of the meteor's ore, they conducted many tests on the small sample they had. During those tests they realise how valuable a discovery they had made. They presented their initial findings and after several gruelling trials and appearances before government they were given full funding to create a massive floating platform-like city to investigate, mine the meteor and research the resulting ore.

Thus the construction of Giga City began a few years later (in early 2172). Though due to a successful Maverick attack (in 2175), Giga City's construction was significantly delayed. It took several extra years to complete the project (with Giga City being fully completed in 2192) and begin the mining process.

Progress was slow at first to extract and produce the newly christened Force Metals, but soon enough researchers began to get more results. The initial results were promising so they kept forging ahead and working on newer and better methods for refining and working with Force Metals. Though results were largely kept secret until years later (until the rebellion in 2210).

After the rebellion though, Force Metal use was clamped down on. Research into it was halted and supplies of existing Force Metals were rounded up and quarantined in secure Hunter facilities.

Force Metals (the refined form of the meteor's ore) provide the user with a powerful boost to their abilities. Each Force Metal contains a massive amount of energy that a reploid can tap into. Different Force Metals give different enhancements.

This gets even more powerful with larger Force Metals or those which have been refined repeatedly. But by using larger or more powerful Force Metals it also accelerates the negative side effects.

While Force Metals tended to give increased capabilities for reploids, some had negative effects… Like for elemental based Force Metals, which gave immunity to one element, would often cause the reploid to increase their weakness to another element. (So a reploid might get gain some immunity to fire, but become weaker to water-based attacks in the process.)

Unfortunately, all Force Metals had a hidden flaw (which became widely apparent in 2210 after the rebellion). Overuse (or prolonged use) of them caused reploids to suffer side effects from glitches to even turning maverick.

This inevitably lead to Force Metal use being abandoned as an energy source. Focus was turned to other sources and research. (Though Giga City remained in place and mined other minerals/resources instead.)

Force Metals never really gained significant usage outside of Giga City (where they were produced). Exports of Force Metals were kept tightly controlled (and often only to Hunter controlled facilities or those sanctioned by Hunters). And when the side effects became known, it effectively halted any chance of Force Metals from ever really entering use.

This meant the bulk of the reploid population never saw or experienced what Force Metals were or could do. And in many cases a lot of Reploids aren't even aware that Force Metals exist.

Force Metal's discovery date was altered (formerly being in 22XX to 2170) to better fit in the timeline. This was done because it would take time for researchers to locate the fallen meteor, mine some of it and research it enough to present to the government in order to gain funding to even build Giga City to begin with. Plus building a city as large as Giga City wasn't something that would easily be accomplished in even a few years.

This also allowed enough time (approximately 18 years) for researchers to look into ways to refine Force Metals and come up with a myriad of different types of Force Metal and uses.