greifensteinite

{{Infobox mineral | name = Greifensteinite | image = Greifensteinite-MA1277056257.jpg | imagesize = 260px | alt = | caption = Greifensteinite (picture size: 3 mm) | category = Phosphate mineral Roscherite group | formula = Ca2Fe2+5Be4(PO4)6(OH)4·6H2O | IMAsymbol = Gfs | strunz = 8.DA.10 | dana = 42.7.7.4 | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = C2/c | unit cell = a = 15.903, b = 11.885 c = 6.677 [Å]; β = 94.68°; Z = 2 | color = Yellow green, olive green, light brown | habit = Prismatic | twinning = | cleavage = Good on {100} (or parting on {100}) | fracture = Uneven | tenacity = brittle | mohs = 4.5 | luster = Vitreous | streak = White, greenish | diaphaneity = Transparent to translucent | gravity = 2.93 | density = | polish = | opticalprop = Biaxial (-) | refractive = nα: 1.624 nβ: 1.634 nγ: 1.638 | birefringence = 0.014 | pleochroism = | 2V = 80° | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = | prop1 = | prop1text = | references = }}

Greifensteinite is beryllium phosphate mineral with formula: Ca2Fe2+5Be4(PO4)6(OH)4·6H2O. It is the Fe2+ dominant member of the roscherite group. It crystallizes in the monoclinic crystal system and typically forms prismatic dark olive green crystals.