Bergenite
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Bergenite is a rare uranyl phosphate of the more specific phosphuranylite group. The phosphuranylite-type sheet in bergenite is a new isomer of the group, with the uranyl phosphate tetrahedra varying in an up-up-down, same-same-opposite (uuduudSSOSSO) orientation. All bergenite samples have been found in old mine dump sites. Uranyl minerals are a large constituent of uranium deposits.[1]
Bergenite | |
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General | |
Category | Uranyl phosphate mineral |
Formula (repeating unit) | Ca2Ba4[(UO2)3O2(PO4)2]3·16(H2O)[1] or (Ba,Ca)2(UO2)3(PO4)2(OH)4·5.5(H2O)[2] |
IMA symbol | Bgn[3] |
Strunz classification | 8.EC.40 |
Crystal system | Monoclinic |
Crystal class | Prismatic (2/m) (same H-M symbol) |
Space group | P21/c |
Identification | |
Color | Yellow to greenish yellow |
Crystal habit | Acicular, tabular |
Mohs scale hardness | 2–3 |
Streak | yellow white |
Diaphaneity | semitransparent |
Density | 4.1 |
Optical properties | Biaxial (-) |
Refractive index | nα = 1.660 nβ = 1.700 - 1.710 nγ = 1.722 |
Birefringence | δ = 0.062 |
Other characteristics | Radioactive, Occurrence: secondary uranium phosphate mineral |
References | [2][4] |
The phosphuranylites are one of the two major groups of the uranyl series, and are the most extensive of the uranium minerals. Uranyl phosphates include 45 different minerals, at least 16 of which belong to the phosphuranylite type topology, including dumontite, vanmeersscheite, upalite, and the most characteristic, phosphuranylite. As explained by Frost et al., the uranyl phosphates display diverse chemical and structural features, which often exhibit the geochemical conditions present during formation.[5]