Vishnevite, or sulfatic cancrinite, is a mineral of the cancrinite group with the chemical formula (Na, Ca, K)6(Si, Al)12O24[(SO4),(CO3), Cl2]2-4·nH2O. It has hexagonal crystals.[1][2]
| Vishnevite |
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 Vishnevite from Scotland |
| General |
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| Category | Tectosilicate |
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Formula
(repeating unit) | (Na,Ca,K)6(Si,Al)12O24[(SO4),(CO3),Cl2]2-4·nH2O |
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| Strunz classification | 9.FB.05 |
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| Crystal system | Hexagonal |
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| Crystal class | Pyramidal (6)
H-M symbol: (6) |
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| Space group | P63 |
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| Unit cell | a = 12.7228(3)
c = 5.198(3) [Å]; Z = 1 |
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| Identification |
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| Color | Colorless, light blue, orange-yellow, white |
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| Cleavage | Perfect |
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| Mohs scale hardness | 5 - 6 |
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| Luster | Vitreous, pearly |
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| Streak | White |
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| Optical properties | Uniaxial (-) |
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| Refractive index | nω = 1.490 - 1.507 nε = 1.488 - 1.495 |
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| Birefringence | δ = 0.002 - 0.012 |
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