beraunite

{{infobox mineral | name = Beraunite | category = Phosphate minerals | image = Beraunite-Kidwellite-214676.jpg | imagesize = 260px | alt = | caption = Crystalline beraunite on green kidwellite, Coon Creek Mine, Polk County, Arkansas, US. Size: 3.4 × 3.3 × 2.8 cm | formula = Fe2+ Fe3+5(OH)5(PO4)4·4H2O | IMAsymbol=Bru | molweight = | strunz = 8.DC.27 | dana = | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = C2/c | unit cell = a = 20.953(8) Å, b = 5.171(1) Å, c = 19.266(4) Å; β = 93.34°; Z = 4 | color = Dull greenish to greenish brown when fresh, may be color banded; reddish brown to hyacinth-red, blood-red on exposure | colour = | habit = Tabular crystals common, may be in coarse radially fibrous aggregates, globular or discoidal, and in crusts | twinning = On {100}, may be interpenetrant | cleavage = On {100}, good | fracture = | tenacity = | mohs = 3–4 | luster = Vitreous, pearly on cleavages, resinous on fractures | streak = Olive-drab when fresh; yellow, brownish yellow on exposure | diaphaneity = Translucent | gravity = 2.8–3.08 (measured); 2.894 (calculated) | density = | polish = | opticalprop = Biaxial (+) | refractive = nα = 1.775 nβ = 1.786 nγ = 1.815 | birefringence = δ = 0.040 | pleochroism = X = pale flesh-pink, yellow, blue-green; Y = pale flesh-pink, yellow, pale olive-green; Z = carnelian-red, reddish brown, olive-green. | 2V = Measured: 30° to 60°, Calculated: 66° | dispersion = | extinction = | length fast/slow = | fluorescence= | absorption = | melt = | fusibility = | diagnostic = | solubility = | other = | alteration = | references = }}

Beraunite is an iron phosphate mineral. It was first described by August Breithaupt for an occurrence in Beraun currently in the Czech Republic. Beraunite occurs as a secondary mineral in iron ore deposits, and as an alteration product of primary phosphate minerals in granite pegmatites.