Earlier today, I read a terrific theory on Diamondhead. Given the current story arc in Nova with the Lifestone Tree gems, it made someone wonder:
Since one of the Lifestone Tree gems created the WWII hero Blue Diamond, is it possible that another one of the same gems is what powered the laser that created Diamondhead?
I think that's a great idea!
The only tweak I'd make is that it might not be a second gem but a fragment of the original one that created Blue Diamond. In BD's origin, an explosion shattered the gem and the shards are what created BD. That would seem to indicate that there were chunks left over and one good sized piece could have been found and used to power the laser.