There used to be a humorous comment about this ore but Zeme removed it because he has no sense of humour whatsoever.Hydrogen is the most abundent resource in the game as it can be found throughout each and every galaxy.
For every 10 Hydrogen Rocks you refine, you get 1 Hydrogen Block back. To refine rocks, you need them to be in a warehouse.
Hydrogen Blocks are the result of 10 refined Hydrogen Rocks. These are generally the most abundant block since Hydrogen rocks are the most abundent in the game.