Created by placing 3-6 Managlass in a Runic Altar, they'd each store 5 or 10 percent of a Mana Pool's capacity. A more condensed version would use Alfglass on a Terrestrial Agglomeration Plate, consuming 25 to 50 percent of a Pool. When thrown into a Mana Pool, the mana that went into it is returned, but the Managlass/Alfglass is not - like a manufactured, much more potent Black Lotus. To prevent loss, the Pool won't absorb it unless it has enough capacity to do so (or is over a Mana Void). Emits light and is (technically) transparent. Despite using Glass as its framework, it'd be harvestable without Silk Touch. Could possibly be crafted into Bricks, Slabs and Stairs, which would still return (a proportional amount of) mana.

Because I want to build houses out of Energon Cubes - I mean, Mana Blocks. Also, giving additional uses to devices (Altars and Plates) is fun.