These Reserves give ores when broken and will respawn after a set amount of time, the time it takes get longer as you go up the tiers of ores
These blocks are placed when a reserve is broken acting as the "recharge" state of the reserve, these block can not be mined
Aetherium Tools are a new tier coming after netherite. Lots of Aetherium ore has to be mined to craft these tools