Board Thread:News and Announcements/@comment-4929778-20160124050717/@comment-27794563-20160304004408

Well firstly Amethyst said in one of the webisodes that gems aren't born as babies they suck up the energy then emerge, but because she had stayed in the ground too long her physical form was ruined so she had to ease it out over the years, in fact she will never truly be the quartz she was meant to be just because of that one mistake,

Based off this we can determine that a gem has a deadline as to when it must emerge or else it turns out like burnt cooking lol.

As for their birth system that has also been explained, gems were made out of a primordial goop that drained life essence from the planet, now in a natural phase this could take around 100-1000 earth years, that is why they made the injectors since gems are made a specific depth in a planet. you can research gem production rates and determine how long it would take the old fashioned way.