# Bararite

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{{Short description|Halide mineral}}
{{Distinguish|barite}}
{{Infobox mineral
| name     = Bararite
| category = [Halide mineral](/source/Halide_mineral)
| boxwidth = 
| boxbgcolor = 
| image    = Bararite.jpg
| imagesize = 
| caption  = Pale pink yellowish crystals of bararite from Shamokin, Northumberland County, Pennsylvania, USA
| formula  = [(NH<sub>4</sub>)<sub>2</sub>SiF<sub>6</sub>](/source/Ammonium_fluorosilicate)
|IMAsymbol=Brr<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref>
| strunz   = 3.CH.10
| system   = [Trigonal](/source/Trigonal)
| class    = Hexagonal scalenohedral ({{overline|3}}m) <br>[H-M symbol](/source/H-M_symbol): ({{overline|3}} 2/m)
| symmetry = ''P''{{overline|3}}m1
| unit cell = a = 5.77&nbsp;Å, c = 4.78&nbsp;Å; Z&nbsp;=&nbsp;1
| color    = White to colorless
| habit    = Tabular, sometimes elongated on [{0001}](/source/Miller_index),<br />also appears in irregularly shaped or [mammillary](/source/Crystal_habit) surfaces that comprise mainly [cryptohalite](/source/cryptohalite)
| twinning  = Interpenetration twins (paddlewheels/darts), axis parallel to {0001}
| cleavage  = [0001] perfect
| fracture  = 
| tenacity  =
| mohs    = 2.5
| luster   = Vitreous
| polish   = 
| refractive = n<sub>ω</sub> = 1.406 ± 0.001,<br />n<sub>ε</sub> = 1.391 ± 0.003
| opticalprop = Uniaxial (-)
| birefringence = 0.015 ± 0.003
| dispersion = 
| pleochroism = 
| fluorescence= 
| absorption =
| streak   = 
| gravity   = 2.152 (synthetic)
| density   = 
| fusibility = 
| diagnostic = 
| solubility = Dissolves in water
| diaphaneity = Transparent
| other    = salty taste
| references = <ref>[https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Bararite Mineralienatlas]</ref><ref name="Palache"/><ref name="Anthony"/><ref name="Christie"/><ref name="Schlemper1"/><ref>[http://www.mindat.org/min-511.html Bararite on Mindat.org]</ref><ref>[http://www.webmineral.com/data/Bararite.shtml Bararite data on Webmineral]</ref>
}}
'''Bararite''' is a natural form of [ammonium fluorosilicate](/source/ammonium_fluorosilicate) (also known as hexafluorosilicate or fluosilicate). It has chemical formula (NH<sub>4</sub>)<sub>2</sub>SiF<sub>6</sub> and [trigonal](/source/Trigonal_crystal_system) crystal structure. This mineral was once classified as part of [cryptohalite](/source/cryptohalite). Bararite is named after the place where it was first described, Barari in Jharia Coal Field, [Dhanbad](/source/Dhanbad), [India](/source/India).<ref name="Palache">Palache, C., Berman, H., and Frondel, C. (1951) Dana’s System of Mineralogy, Volume II: Halides, Nitrates, Borates, Carbonates, Sulfates, Phosphates, Arsenates, Tungstates, Molybdates, etc. John Wiley and Sons, Inc., New York, 7th edition.</ref> It is found at the [fumarole](/source/fumarole)s of [volcano](/source/volcano)es ([Vesuvius](/source/Vesuvius), [Italy](/source/Italy)), over [burning coal seams](/source/Coal_seam_fire) (Barari, India), and in burning piles of [anthracite](/source/anthracite) ([Pennsylvania](/source/Pennsylvania), U.S.). It is a [sublimation](/source/Volcanic_sublimate) product that forms with cryptohalite, [sal ammoniac](/source/sal_ammoniac), and [native sulfur](/source/native_sulfur).<ref name="Anthony">Anthony, J.W., Bideaux, R.A., Bladh, K.W., and Nichols, M.C. (1997) Handbook of Mineralogy, Volume III: Halides, Hydroxides, Oxides. Mineral Data Publishing, Tucson.
*[http://www.handbookofmineralogy.org/pdfs/BARARITE.pdf link to bararite] {{Webarchive|url=https://web.archive.org/web/20160401193238/http://www.handbookofmineralogy.org/pdfs/Bararite.pdf |date=2016-04-01 }}
*[http://www.handbookofmineralogy.org/pdfs/CRYPTOHALITE.pdf link to cryptohalite] {{Webarchive|url=https://web.archive.org/web/20211202010021/http://www.handbookofmineralogy.org/pdfs/Cryptohalite.pdf |date=2021-12-02 }}</ref>

==History==
A. Scacchi first discovered cryptohalite in 1873.<ref name="Palache"/> It appeared in a volcanic sublimate from the [Vesuvian eruption](/source/Mount_Vesuvius) of 1850. In 1926, W.A.K. Christie reported his own chemical study. A microscope was used to pick out enough material for analysis. Distilling with [sodium hydroxide](/source/sodium_hydroxide) (NaOH) produced [ammonia](/source/ammonia) (NH<sub>3</sub>). The anions of [hexafluorosilicic acid](/source/hexafluorosilicic_acid) (H<sub>2</sub>SiF<sub>6</sub>) precipitated as [potassium fluorosilicate](/source/potassium_fluorosilicate) (K<sub>2</sub>SiF<sub>6</sub>). [Barium sulfate](/source/Barium_sulfate) (BaSO<sub>4</sub>) was thrown into the filtrate, and then [calcium fluoride](/source/calcium_fluoride) (CaF<sub>2</sub>). Christie found 20.43% (NH<sub>4</sub>)<sup>+</sup> and 78.87% (SiF<sub>6</sub>)<sup>2−</sup>.<ref name="Christie">Christie, W.A.K. (1926) An Occurrence of Cryptohalite (Ammonium Fluosilicate). Records of the Geological Survey of India, 59, 233.</ref>

Bararite is named after [Barari](/source/Barari), a [locality](/source/locality_(India)) in [India](/source/India). This was where the species was first completely described. Earlier, bararite was recognized as part of mixtures with [cryptohalite](/source/cryptohalite).<ref name="Palache"/> However, it did not receive its own name until 1951.<ref name="Palache"/><ref name="Fleischer">Fleischer, M. (1952) [http://www.minsocam.org/ammin/AM37/AM37_359.pdf "New Mineral Names"]. American Mineralogist, 37, 359–362.</ref> The [East Indian Coal Company](/source/Coal_mining_in_India) provided the sample that Christie used to evaluate bararite.<ref name="Christie"/>

Bararite has not received a quantitative chemical analysis in its natural form.<ref name="Anthony"/> Christie received far too little for more than ''qualitative'' analysis through microchemistry. He utilized F. Emich's methods with [capillary tube](/source/Capillary_action) [centrifuge](/source/centrifuge)s.<ref name="Christie"/>

==Structure==
Bararite is the beta, [trigonal](/source/Trigonal_crystal_system) (scalenohedral) form of [ammonium hexafluorosilicate](/source/Ammonium_fluorosilicate). Its symmetry is {{overline|3}}2/m.<ref name="Anthony"/> The [space group](/source/space_group) is P{{overline|3}}m1. The ''a''-axes in the unit cell are 5.784 ± 0.005&nbsp;Å ([angstrom](/source/angstrom)s), and the ''c''-axis is 4.796 ± 0.006 Å. The unit lattice is primitive.<ref name="Schlemper1">Schlemper, E.O. and Hamilton, W.C. (1966) [http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JCPSA6000045000001000408000001&idtype=cvips&gifs=yes On the Structure of Trigonal Ammonium Fluorosilicate]. Journal of Chemical Physics, 45, 408–409.
*[http://rruff.geo.arizona.edu/AMS/viewJmol.php?id=12826 Unit cell diagram based on this article]</ref><ref>Anthony et al. (1997) and Palache et al. (1951) use outdated information for the crystal axes. The information in these handbooks is linked ultimately to two articles by Gossner and Krauss from 1934, in Zeitschrift für Kristallographie. The replacement source, Schlemper and Hamilton (1966), is cited not just by this article but also Boldyreva et al. (2007).</ref> (Note: Data for the space group come from synthetic crystals.) Cryptohalite has the [cubic](/source/Cubic_crystal_system) (isometric) crystal structure and corresponds to the alpha form. Both minerals have the chemical formula [(NH<sub>4</sub>)<sub>2</sub>SiF<sub>6</sub>](/source/Ammonium_fluorosilicate). The [halide](/source/halide)s of form ''A<sub>m</sub>BX''<sub>6</sub> fall into two groups: [hieratite](/source/hieratite) and [malladrite](/source/malladrite). The hieratite group is isometric whereas the malladrite is hexagonal.<ref name="Palache"/>

The (SiF<sub>6</sub>)<sup>2−</sup> is [octahedral](/source/Octahedral_molecular_geometry)—one [fluorine](/source/fluorine) atom at each [vertex](/source/Vertex_(geometry)).<ref name="Schlemper2">{{cite journal|doi=10.1063/1.1727071|title=Structure of Cubic Ammonium Fluosilicate: Neutron-Diffraction and Neutron-Inelastic-Scattering Studies|year=1966|last1=Schlemper|first1=Elmer O.|journal=The Journal of Chemical Physics|volume=44|pages=2499–2505|issue=6|bibcode = 1966JChPh..44.2499S }}</ref> In bararite, the (NH<sub>4</sub>)<sup>+</sup>’s are [trigonally](/source/Trigonal_planar_molecular_geometry) coordinated. They all appear at sites of C<sub>''3v''</sub> (3m) symmetry. The (NH<sub>4</sub>)<sup>+</sup> has 12 fluorine neighbors, which form four triangles. Three of these triangles are [isosceles](/source/Triangle). These triangles themselves form a triangle—around the [3-fold axis](/source/Rotational_symmetry) containing the nitrogen atom. One triangle is [equilateral](/source/Triangle). Its [symmetry axis](/source/Rotational_symmetry) is the same axis that goes through the nitrogen atom.<ref name="Oxton">Oxton, I.A., Knop, O., and Falk, M. (1975) [http://article.pubs.nrc-cnrc.gc.ca/ppv/RPViewDoc?issn=1480-3291&volume=53&issue=22&startPage=3394 "Infrared Spectra of the Ammonium Ion in Crystals"]. II. The Ammonium Ion in Trigonal Environments, with a Consideration of Hydrogen Bonding. Canadian Journal of Chemistry, 53, 3394–3400.</ref> (For structural diagrams, see link to unit cell<ref name="Schlemper1"/> and downloadable articles<ref name="Oxton"/><ref name="Boldyreva"/> in “References.”)

The silicon atoms of cryptohalite, α-(NH<sub>4</sub>)<sub>2</sub>SiF<sub>6</sub> (alpha), have [cubic close(st) packing](/source/Sphere_packing) (CCP). A third form (gamma, γ) of (NH<sub>4</sub>)<sub>2</sub>SiF<sub>6</sub> uses [hexagonal close(st) packing](/source/Sphere_packing) (HCP). Bararite, β-(NH<sub>4</sub>)<sub>2</sub>SiF<sub>6</sub>, utilizes [https://web.archive.org/web/20090526142134/http://www.polymorf.net/matter4.htm hexagonal primitive] (HP) packing. Layers with distorted octahedral gaps separate those with the [anion](/source/anion)s. The (NH<sub>4</sub>)<sup>+</sup> [ions](/source/Ion_(chemistry)) appear a little below and above the (SiF<sub>6</sub>)<sup>2−</sup>. In all three phases, 12 fluorine atoms neighbor the (NH<sub>4</sub>)<sup>+</sup>. Distances range from about 3.0 to 3.2 Å.<ref name="Boldyreva">{{cite journal|author=Boldyreva, E.V. |author2=Shakhtshneider, T.P |author3=Sowa, H. |author4=Ahsbas, H. |name-list-style=amp |year=2007|title=Effect of hydrostatic pressure up to 6&nbsp;GPa on the crystal structures of ammonium and sodium hexafluorosilicates, (NH<sub>4</sub>)<sub>2</sub>SiF<sub>6</sub> and Na<sub>2</sub>SiF<sub>6</sub>; a phase transition in (NH<sub>4</sub>)<sub>2</sub>SiF<sub>6</sub> at 0.2–0.3 GPa|journal=Zeitschrift für Kristallographie|pages=23–29|doi=10.1524/zkri.2007.222.1.23|volume=222|issue=1 |bibcode = 2007ZK....222...23B |s2cid=97174719 }}</ref> The (NH<sub>4</sub>)<sup>+</sup> has no free rotation. It only [librates](/source/Libration_(molecule)) (oscillates)—at least when vibrationally excited.<ref name="Oxton"/>

As a [salt](/source/Salt_(chemistry)), bararite is an [ionic compound](/source/ionic_compound). The ions, of course, have [ionic bond](/source/ionic_bond)ing. The atoms of [polyatomic ion](/source/polyatomic_ion)s are held together [covalently](/source/Covalent_bond). The orientation of (NH<sub>4</sub>)<sup>+</sup> is sustained by four trifurcated (three-branch) [hydrogen bond](/source/hydrogen_bond)s. These bonds point toward the triangles containing the 12 fluorine neighbors. Three H bonds are equivalent. The fourth bond, pointing toward the equilateral triangle, has a shorter distance.<ref name="Oxton"/>

The intermolecular distances between fluorine atoms are smaller in bararite (3.19 and 3.37&nbsp;Å) than cryptohalite. In cryptohalite, each anion is coordinated to 12 others. Bararite has (2+6)-fold coordination. The two Si-Si distances between layers (4.796 ± 0.006 Å) do not equal the six within a layer (5.784 ± 0.005&nbsp;Å). Bararite is more compressible along the ''c''-axis than the ''a''-axis.<ref name="Boldyreva"/>

Bararite has no known [solution](/source/Solid_solution) or [exsolution](/source/exsolution), but it is always mixed with other substances ([cryptohalite](/source/cryptohalite), [sal ammoniac](/source/sal_ammoniac), and [sulfur](/source/sulfur)).<ref name="Anthony"/> Due to thermal motion, atomic behavior of ammonium salts can be very hard to evaluate.<ref name="Schlemper2"/> The anions, however, are ordered and have no unusual motion from heat.<ref name="Schlemper1"/>

A third form of (NH<sub>4</sub>)<sub>2</sub>SiF<sub>6</sub> was discovered in 2001 and identified with the 6mm symmetry ([hexagonal](/source/Hexagonal_crystal_system)).<ref name="Boldyreva"/> In all three arrangements, the (SiF<sub>6</sub>)<sup>2−</sup> [octahedra](/source/VSEPR_theory) come in layers. In the cubic form (cryptohalite), these layers are perpendicular to [[Miller index|[111]]].<ref name="Boldyreva"/> In the trigonal (bararite) and hexagonal (gamma, γ) forms, the layers are perpendicular to the c-axis.<ref name="Boldyreva"/> (Note: Trigonal crystals are part of the hexagonal group. But not all hexagonal crystals are trigonal.<ref name="Klein"/>)

Although bararite was claimed to be [metastable](/source/Metastability) at [room temperature](/source/room_temperature),<ref name="Schlemper2"/> it does not appear one [polymorph](/source/Polymorphism_(materials_science)) has ever turned into another.<ref name="Boldyreva"/> Still, bararite is fragile enough that grinding it for [spectroscopy](/source/spectroscopy) will produce a little cryptohalite.<ref name="Oxton"/> Even so, ammonium fluorosilicate assumes a trigonal form at pressures of 0.2 to 0.3 giga-pascals (GPa). The reaction is irreversible. If this phase is not bararite, it is at least very closely related.<ref name="Boldyreva"/>

The hydrogen bonding in (NH<sub>4</sub>)<sub>2</sub>SiF<sub>6</sub> allows this salt to change phases in ways that normal salts cannot. Interactions between cations and anions are especially important in how ammonium salts change phase.<ref name="Boldyreva"/>

==Physical properties==
Bararite forms [tabular crystals](/source/Crystal_habit). They are flattened, sometimes elongated, on [{0001}](/source/Miller_index) (perpendicular to ''c'').<ref name="Palache"/> Christie reported tiny, transparent crystals of bararite that looked like paddlewheels and darts. Each had four barbs at 90°. The crystals reached up to 1&nbsp;mm long, the barbs up to 0.2&nbsp;mm wide. They were [interpenetration twins](/source/Crystal_twinning), the twin axis perpendicular to the ''c''-axis.<ref name="Christie"/> Visually, [cryptohalite](/source/cryptohalite) crystals are almost impossible to discern from [sal ammoniac](/source/sal_ammoniac) (NH<sub>4</sub>Cl).<ref name="Barnes">Barnes, J. and Lapham, D. (1971) Rare Minerals Found in Pennsylvania. Pennsylvania Geology, 2, 5, 6–8.</ref> Inclusions of bararite in cryptohalite can be seen only with plane-polarized light.<ref name="Lapham">Lapham, D.M., Barnes, J.H., Downey, W.F., Jr., and Finkelman, R.B. (1980) Bararite. Mineralogy associated with burning anthracite deposits of eastern Pennsylvania. Pennsylvania Geological Survey: Mineral Resource Report, 78, 45–47.</ref>

Bararite has perfect [cleavage](/source/Cleavage_(crystal)) on the {0001} plane. The [hardness](/source/Mohs_scale_of_mineral_hardness) is probably {{frac|2|1|2}}.<ref name="Palache"/> The anions (as already shown) are bonded much more strongly within layers than between layers. Also, [ionic bond](/source/ionic_bond)s are not the strongest bonds, and [halide](/source/halide)s cannot normally scratch glass plates.<ref name="Klein">Klein, C. and Dutrow, B. (2008) The 23rd Edition of the Manual of Mineral Science. John Wiley & Sons, Hoboken, NJ.</ref>

Bararite has a measured [density](/source/density) of 2.152&nbsp;g/mL (synthetic)—but a calculated density of 2.144&nbsp;g/mL. It tastes salty, and it [dissolves](/source/Solubility) in water. Its [luster](/source/Lustre_(mineralogy)) is vitreous (like glass). Bararite is white to colorless.<ref name="Palache"/> These properties are similar to [halite](/source/halite) (NaCl)<ref name="Klein"/>—which gave the [halide group](/source/halide_group) its name.

Whereas cryptohalite belongs to the [isotropic](/source/Isotropy) optical class, bararite is uniaxial negative.<ref name="uniaxial">To learn what makes a uniaxial crystal, visit [http://www.tulane.edu/~sanelson/eens211/uniaxial_minerals.htm Introduction to Uniaxial Minerals].</ref><ref name="Palache"/> At 1.391 ± 0.003, the refractive index through ''c'' is smaller than through ''a'' (1.406 ± 0.001).<ref name="Christie"/> The ''c''-axis in bararite is shorter than the ''a''-axes (see “Structure”). Furthermore, only this path lets light hit nothing but the same ion in the same orientation (all the layers have the same structure and orientation<ref name="Boldyreva"/>).

Bararite has about a 6% greater density than cryptohalite.<ref name="Boldyreva"/> As discussed before, its structure is more packed. This substance can be produced easily from [aqueous solution](/source/aqueous_solution),<ref name="Palache"/> but only below 5&nbsp;°C (41&nbsp;°F) will pure bararite form.<ref name="Palache"/><ref name="Gossner">Gossner, B. (1903) Ammoniumsiliciumfluorid. Zeitschrift für Kristallographie, 38, 147–148.</ref> Above 13&nbsp;°C (55&nbsp;°F), almost pure cryptohalite emerges.<ref name="Palache"/><ref name="Christie"/> Bararite [sublimes](/source/Sublimation_(chemistry)) without leaving residue.<ref name="Palache"/>

==Geologic occurrence==
In nature, bararite appears with cryptohalite, [sal ammoniac](/source/sal_ammoniac), and native [sulfur](/source/sulfur).<ref name="Christie"/><ref name="Barnes"/> It is found over a [burning coal seam](/source/Coal_seam_fire) in Barari, [India](/source/India),<ref name="Christie"/> and as a sublimation product in [Vesuvius](/source/Vesuvius), [Italy](/source/Italy), at [fumarole](/source/fumarole)s (opening in or near a [volcano](/source/volcano) where hot [sulfur](/source/sulfur)ous gases come out).<ref name="Anthony"/><ref name="Scacchi">Scacchi, A. (1874) [https://books.google.com/books?id=ykUsAAAAYAAJ&pg=RA1-PA179 "Appendice alle contribuzioni mineralogiche sull’ incendio vesuviano del 1872"]. Rendiconto dell’Accademia delle scienze fisiche e matematiche (sezione della Società reale di Napoli), 8, 179–180.</ref> It also is found in the [United States](/source/United_States), in [Pennsylvania](/source/Pennsylvania). It appears in [burning piles](/source/Coal_seam_fire) of [anthracite](/source/anthracite) (highest grade of coal)—again as a sublimation product.<ref name="Barnes"/>

Christie found translucent [arborescent](/source/Crystal_habit) (treelike) crystals, with vitreous [luster](/source/Lustre_(mineralogy)). He found white, opaque lumps that were a mixture of [(NH<sub>4</sub>)<sub>2</sub>SiF<sub>6</sub>](/source/Ammonium_fluorosilicate) with [SiO<sub>2</sub>](/source/Silicon_dioxide). They were irregularly shaped but usually had a [mammillary](/source/Crystal_habit) surface (several convex surfaces smoothly rounded). These hold primarily [cryptohalite](/source/cryptohalite) but also some bararite.<ref name="Christie"/> In Pennsylvania, bararite normally comes as tiny inclusions in cryptohalite crystals.<ref name="Barnes"/><ref name="Lapham"/> It appears that first, bararite forms through direct sublimation. Afterward, it quickly changes to cryptohalite.<ref name="Lapham"/>

In Barari, [burning-coal gases](/source/Coal_seam_fire) go through a [dike](/source/Dike_(geology)) (igneous intrusion) of [mica](/source/mica) and [peridotite](/source/peridotite). The [sulfur dioxide](/source/sulfur_dioxide) must attack [apatite](/source/apatite) in the dike, which produces [hydrofluoric acid](/source/Hydrogen_fluoride) that attacks the abundant [silicate](/source/silicate)s. [Silicon fluoride](/source/Silicon_tetrafluoride) is formed. [Ammonia](/source/Ammonia) also comes from [burning coal](/source/Coal_seam_fire). From there, [ammonium fluorosilicate](/source/ammonium_fluorosilicate) can form. A slight excess of [ammonia](/source/ammonia) could lead to the white lumps of [silica](/source/Silicon_dioxide) and [cryptohalite](/source/cryptohalite). Bararite and cryptohalite in their pure forms, for the most part, grow out of these nodules. Recrystallization from the rain is probably responsible.<ref name="Christie"/>

[Fluorosilicate](/source/Fluorosilicate) minerals are [thermodynamically unstable](/source/Chemical_stability) in soil.<ref name="Elrashidi">Elrashidi, M.A. and Lindsay, W.L. (1986) [http://journals.lww.com/soilsci/Abstract/1986/04000/Chemical_Equilibria_of_Fluorine_in_Soils__A.4.aspx Chemical Equilibria of Fluorine in Soils: A Theoretical Development]. Soil Science: An Interdisciplinary Approach to Soil Research, 141, 274–280.</ref> Still, intense heat promotes the formation of (NH<sub>4</sub>)<sub>2</sub>SiF<sub>6</sub> to some degree—as seen in some experiments by Rehim. But this [compound](/source/Chemical_compound) will [break up](/source/Thermal_decomposition) at 320 to 335&nbsp;°C.<ref name="Rehim">{{cite journal|doi=10.1007/BF01915512|title=Thermal study of synthesis of cryptohalite|year=1992|last1=Rehim|first1=A. M. Abdel|journal=Journal of Thermal Analysis|volume=38|pages=475–486|issue=3|s2cid=95930085}}</ref> Both [burning coal](/source/Coal_seam_fire)<ref name="Christie"/><ref name="Barnes"/> and [volcano](/source/volcano)es are important sources of [SO<sub>2</sub>](/source/Sulfur_dioxide) and [SiF<sub>4</sub>](/source/Silicon_tetrafluoride).<ref name="Mori">Mori, T., Sato, M., Shimoike, Y., and Notsu, K. (2002) [http://www.terrapub.co.jp/journals/EPS/pdf/2002/5403/54030249.pdf "High SiF<sub>4</sub> ratio detected in Satsuma-Iwojima volcano’s plume by remote FT-IR observation"]. Earth Planets Space, 54, 249–256.</ref>

==Chemical properties and uses==
[Fluorosilicic acid](/source/Hexafluorosilicic_acid) and its salts are poisonous.<ref name="Wiberg">Wiberg, E., Wiberg, N., and Holleman, A.F. (2001) Inorganic chemistry. Academic Press, San Diego.</ref> [Ammonium fluorosilicate](/source/Ammonium_fluorosilicate), however, is very rare in nature<ref name="Barnes"/> and apparently much easier to [synthesize](/source/Chemical_synthesis).<ref name="Palache"/>

==References==
{{reflist|30em}}

==External links==
*[http://rruff.geo.arizona.edu/AMS/amcsd.php AMCSD search engine] (cannot link directly to result)
*[http://www.tulane.edu/~sanelson/eens211/uniaxial_minerals.htm Introduction to Uniaxial Minerals]

Category:Ammonium minerals
Category:Silicon minerals
Category:Fluorine minerals
Category:Trigonal minerals
Category:Minerals in space group 164

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Adapted from the Wikipedia article [Bararite](https://en.wikipedia.org/wiki/Bararite) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Bararite?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.