Here is the iron(II) sulfate heptahydrate crystals which I made from steel nails. There were some other metals in those nails, so you can see impurities of different color (the green crystals are iron(II) sulfate heptahydrate).
Iron(II) sulfate crystals | Ecency
My Entry for Secrets of Organ Playing Improvisation Contest Week 3hexacyanoferrate ·
