Hopeite

Hopeite is a hydrated zinc phosphate with formula: Zn₃(PO₄)₂·4H₂O. It is a rare mineral used mainly as a collectors specimen.

Hopeite
Hopeite Belgium – Type locality
General
Category	Phosphate minerals
Formula	Zn3(PO4)2·4H2O
IMA symbol	Hop[1]
Strunz classification	8.CA.30
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pnma
Identification
Formula mass	458.17 g/mol
Color	Colorless, gray white, yellow, white, light yellow
Crystal habit	Encrustations – Forms crust-like aggregates on matrix. Prismatic – crystals shaped like slender prisms (e.g. tourmaline). Reniform – kidney-like in shape (e.g. hematite).
Cleavage	[100] Perfect, [010] good, [001] poor
Fracture	Uneven – flat surfaces (not cleavage) fractured in an uneven pattern
Mohs scale hardness	3–3.5
Luster	Vitreous (glassy)
Streak	White
Specific gravity	3
Optical properties	Biaxial (−), a = 1.572–1.574, b = 1.582–1.591, g = 1.59–1.592
Other characteristics	Non-radioactive, non-magnetic

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'.^[2]