Like the other 2 cards in this vertical cycle, drop this a rarity, lose etb effect and add "~doesn't untap during your next untap step to the end of the mana production ability. You could also keep etb ability & make all 3 cards cost, produce with them getting better as you go up in rarity in terms of howe often you can use them.

could also go, Common cost , produce , uncommon , rare etc, lots of ideas/space here. Cards are OK as is though.

­Worn Powerstone is already a card though. The idea was (in terms of my setting and story for the set) that (spoiler) the Thran created the plane (being an ancient and advanced civilization) and part of their genius was the Powerstones (I was just using Worn Powerstone as a guidline, reasoning that if there was a worn powerstone wouldn't their be others in better/worse condition?)

Fair enough, disregard my ramblings then.

Nice idea to expand an existing card into a cycle.

Ramblings are welcome. Like you said lots of design space. :D