Bararite
Bararite is a natural form of ammonium fluorosilicate (also known as hexafluorosilicate or fluosilicate). It has chemical formula (NH4)2SiF6 and trigonal crystal structure. This mineral was once classified as part of cryptohalite. Bararite is named after the place where it was first described, Barari, India. It is found at the fumaroles of volcanoes (Vesuvius, Italy), over burning coal seams (Barari, India), and in burning piles of anthracite (Pennsylvania, U.S.). It is a sublimation product that forms with cryptohalite, sal ammoniac, and native sulfur.
| Bararite | |
|---|---|
Pale pink yellowish crystals of bararite from Shamokin, Northumberland County, Pennsylvania, USA | |
| General | |
| Category | Halide mineral |
| Formula (repeating unit) | (NH4)2SiF6 |
| IMA symbol | Brr |
| Strunz classification | 3.CH.10 |
| Crystal system | Trigonal |
| Crystal class | Hexagonal scalenohedral (3m) H-M symbol: (3 2/m) |
| Space group | P3m1 |
| Unit cell | a = 5.77 Å, c = 4.78 Å; Z = 1 |
| Identification | |
| Color | White to colorless |
| Crystal habit | Tabular, sometimes elongated on {0001}, also appears in irregularly shaped or mammillary surfaces that comprise mainly cryptohalite |
| Twinning | Interpenetration twins (paddlewheels/darts), axis parallel to {0001} |
| Cleavage | [0001] perfect |
| Mohs scale hardness | 2.5 |
| Luster | Vitreous |
| Diaphaneity | Transparent |
| Specific gravity | 2.152 (synthetic) |
| Optical properties | Uniaxial (-) |
| Refractive index | nω = 1.406 ± 0.001, nε = 1.391 ± 0.003 |
| Birefringence | 0.015 ± 0.003 |
| Solubility | Dissolves in water |
| Other characteristics | salty taste |
| References | |
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