Zincoberaunite

Zincoberaunite is an iron and zinc phosphate mineral, the Zn analogue of beraunite. It was first described by Chukanov et al. for an occurrence in Hagendorf Sud pegmatite in Germany.^[3] Zincoberaunite occurs as a secondary mineral as an alteration product of primary phosphate minerals in granite pegmatites.

Zincoberaunite
General
Category	Phosphate minerals
Formula	ZnFe3+5(OH)5(PO4)4·6H2O
IMA symbol	Zbru[1]
Strunz classification	8.DC.27
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/c
Unit cell	a = 20.837(2) Å, b = 5.1624(4) Å, c = 19.250(1) Å; β = 93.252(5)°
Identification
Color	Light gray, light greenish yellow
Crystal habit	Fiber, capillary or prismatic microcrystals
Mohs scale hardness	3–4
Luster	VSilky, vitreous
Diaphaneity	Translucent
Specific gravity	2.94
Optical properties	Biaxial (+)
Refractive index	nα = 1.745 nβ = 1.760 nγ = 1.770
Birefringence	δ = 0.025
2V angle	Measured: 80°
References	[2]

Beraunite crystallizes in the monoclinic crystal system with point group 2/m. Beraunite's formula is Zn Fe³⁺₅(OH)₅(PO₄)₄·4H₂O.

Occurrence

Zincoberaunite has been located so far in two localities in the world, the type locality, and Krasno, near Horní Slavkov (Czech Republic). It appears in two paragenesis, as an alteration of other phosphates in pegmatites: in one with jungle, phosphophyllite and mitridatite and in another with flurlite, plimerite, beraunite rich in zinc, schoonerite, parascholzite, robertsite and altered phosphophyllite. However, it is likely that a detailed study of the zinc-rich beraunite specimens will allow locating other localities for the zincoberaunite.

Physical and chemical properties

Zincoberaunite contains Zn instead of ferrous iron. Before it was characterized as an independent species, specimens with a high zinc content had been found, but since the iron content was higher, they had been considered as varieties. In addition to the elements indicated in the formula, it contains small amounts of magnesium and calcium. In the type locality it appears as pale gray capillary microcrystals forming silky-looking aggregates. In a second locality it has been found as prismatic microcrystals with compositional zoning.^[4]