When a star is too small to become a neutron star or to go supernova, the most amount of pressure it can generate only allows it to conduct nuclear fusion to the element carbon. When all hydrogen converts to carbon, no longer able to sustain the reaction, the star transforms into a "white dwarf". It does so when all of the carbon collapses in on its own mass and is subjected to all the pressure and power that an entire star worth of gravity can compress it with. What is one left with?



A diamond.



An immense, perfect, pure diamond...billions of years old and possessing all the latent energy of an entire star worth of nuclear fission reactions.



So that's how the Gem race was "born".