Hm... Well the 'split' gem idea would be an 'ancient' kind of gem if that makes sense, back when the Gem Empire was conquering worlds left and right. Formed from a neutron star or something. (I'm really into cosmetology and quantum physics atm. And Neutron stars are cool as hell.) I think I could only use that one if they are already on Earth and wake up from an ancient gem stasis ship due to the people landing on Earth. 

Marry meanwhile can fit in wherever.

Up to you. Split gem would have a super offensive and super defensive halves, Marry would just be portal mania.