Mini Game Purpose?

So what is the point of doing it? I don't see anything on the page that mentions the benefit of playing with the mini-game.

Skill description:

“	And, if you are lucky, you will also be able to create precious gems such as diamonds or new metals never seen before in Erinn.	„

Mini-game section:

“	The range of the green sections will narrow at rank 9 and rank 5, however the potential rewards are increased.	„

“	The outcome of the minigame merely affects the item produced and not the success rate itself.	„

Skill summary: http://puu.sh/k0gIE/490e1a156c.png

This talk page: Talk:Metal Conversion#Outcomes

I see. However, I find it a rather vague explanation, as there is no explicit mention of the mini game's purpose.

Also is it necessary to have all four markers spot on or will one just suffice?

I'm pretty all it does is affect whether you get the extra mats such as tin or gems. From my experience you have to get all 4 green spots in order to have a chance of an extra mat.

Roughly how much extra ores/gems do you get from it?

As far as I can tell, the chance of getting special ores or gems is 0% unless you get all four green sections. However, I almost always got all four green sections and really didn't pay attention to my inventory to see when they bonus results were given to me. As such, I'm not very confident on my answer.