Nabimusaite is a very rare mineral with formula KCa12(SiO4)4(SO4)2O2F.[2] Its structure, as in case of similar aradite and zadovite, is a derivative of the one of hatrurite.[4] Nabimusaite gives its name to the nabimusaite group.[5] The mineral was found in a pyrometamorphic rock of the Hatrurim Formation, a site known for the natural pyrometamorphism. It is interpreted to have formed due to interaction of a precursor assemblage with sulfate-rich melt.[2] Nabimusaite is potassium- and fluorine-analogue of dargaite.[6]
Nabimusaite | |
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General | |
Category | Silicate mineral, nesosilicate |
Formula (repeating unit) | KCa12(SiO4)4(SO4)2O2F |
IMA symbol | Nbm[1] |
Crystal system | Trigonal |
Crystal class | Hexagonal scalenohedral (3m) H-M symbol: (3 2m) |
Space group | R3m |
Unit cell | a = 7.19, b = 7.19 c = 41.25 [Å] (approximated); Z = 3 |
Identification | |
Color | Colorless |
Cleavage | (001), imperfect |
Tenacity | Brittle |
Mohs scale hardness | 5 |
Luster | Vitreous |
Streak | White |
Density | 3.12 (calculated) (approximated) |
Optical properties | Uniaxial (-) |
Refractive index | nω=1.64, nε=1.64 (approximated) |
References | [2][3] |
Nabimusaite was discovered in nodules composed of larnite and ye'elimite, in a rock formed due to pyrometamorphism.[2]
Nabimusaite is impure as it has a phosphorus admixture.[2]
Crystal structure of nabimusaite is modular. It is of antiperovskite type. It is composed of hatrurite-like modules [Ca12(SiO4)4O2F]3+ anions in octahedral and cations in tetrahedral coordination with [K(SO4)2]3 modules. The two modules are mutually intercalated.[2]
Nabimusaite is suggested to result from interaction of a melt, rich in potassium and sulfate, with earlier minerals (ellestadite and larnite).[2]