Star Crystal

A magical mineral that is now deposited in veins where groundwater runs through rocks that have been exposed over time to significant amounts of magic (be that fairy glamor/domain magic, or wizard magic under the Wizard's towers/university, or the magic of the Underdark folk, or even under/around a vault). But as mineral deposition takes time, I'm going to seed the world with lots of these veins, more or less randomly. Currently, there's a higher density of lodes/veins in the Underdark, since its inhabitants likely will not see the stars for a long time, but I imagine intensely magical places like the Courts or the Druidic Groves are going to naturally grow more crystals than other places over time These crystals have a habit (shape) similar to marcasite (mineralogists call this a coxcomb crystal habit, look up coxcomb marcasite it's weird & cool)   The crystals have the translucence/opacity of gummies (but obviously not the texture), and the color of the Ring Star that is closest to the north pole at a given moment. If two stars are equidistant, then the color of the crystal becomes a gradient between the two   Apparently the different colors have different flavors/spices/vibes to the rock-eating Underdark folk   Trying to use them to power alchemical rituals (because they're sorta like crystals made of weak magic congealed into a lattice) probably just causes them to shatter into a bunch of tiny pieces with very low magical yield, if any