Hopeite is a hydrated zinc phosphate with formula: Zn3(PO4)2·4H2O. It is a rare mineral used mainly as a collectors specimen. Hopeite crystallizes in the orthorhombic system with prismatic, vitreous white to yellow crystals. It also forms druzy encrustations and reniform (kidney-shaped) masses. The related mineral parahopeite, which has the same composition but different crystal structure, is triclinic. The minerals are formed through oxidation of sphalerite by the presence of phosphate-rich solutions. It was first described in 1822 from Moresnet, Liège Province, Belgium and is named after Scottish chemist, Thomas Charles Hope (1766–1844) of the University of Edinburgh. It has been found in Zambia associated with lazulite. Hopeite is one of the two conversion minerals arising from the application of the rust converter 'Fertan'.