There's a cauldron on one of my sims' lot and they just use it for cooking. They keep getting those stones in their inventory. It's quite annoying but not really as game breaking as some of the other bugs (please save Discover university, I'd love to play it again) so I'm fine with this for now.
I wish it was something specific sims had to do to get the glimmerstone, like really consciously do something that aims to receive the magic stone. I don't think cooking mac and cheese should be the magic trick to get the stone but that's just my opinion.
August - last edited August
I play The Sims 4 on PS 4. I encounter the same issue. It's one of the results of having a spellcaster in the direct family. Also I have Unregistered Alien/spellcaster who can cast spells too. But recently had a little merman born into the family with a weak bloodline from having a spellcaster parent. As a kid, he has a Glimmerstone. I've managed to have unregistered alien/spellcasters and with the cheats, they have mermaid abilities and tail. There's two downsides. While exiting the water, his tail will emerge and he'll walk on his fins. Or He'll swim the sand as easy as the water in merman form. I have him remove his diguise to get back to a natural sim.