Maybe try copper sulphate?

https://crystalverse.com/best-way-to-grow-copper-sulfate-cry...

Crystal growth has been on here before. Let me see if I can find a link or two...

https://news.ycombinator.com/item?id=31105320

https://news.ycombinator.com/item?id=30487511

https://news.ycombinator.com/item?id=29779923

https://news.ycombinator.com/item?id=29255511