Main article: Tutton's salts.
Tutton's salts - double salts, water hydrates of sulfates with common formula (Me+)2Me2+(SO4)2 · 6H2O, where Me+ is alkaline metal (potassium, cesium, rubidium), monovalent metal thallium or ammonium ion and Me2+ is bivalent metal (iron, copper, nickel, cobalt, manganese, magnesium, zinc, vanadium, cadmium). Salts based on sodium and lithium doesn`t forms because they have too small iron radius.
All Tutton's salts are highly or moderately soluble in water and have monoclinic crystal system.
List of suitable for crystal growing Tutton's salts is presented below.