# Stillwaterite

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{{Infobox mineral
| name        = Stillwaterite
| category    = Arsenide mineral
| boxwidth    = 
| boxbgcolor  = 
| image       = 
| imagesize   = 
| caption     = 
| formula     = Pd<sub>8</sub>As<sub>3</sub>
| IMAsymbol   = Slw<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>
| system      = [Trigonal](/source/Trigonal)
| class       = Pyramidal (3) <br/> or rhombohedral ({{overline|3}}) <br/>[H-M symbol](/source/H-M_symbol): (3 or {{overline|3}})
| symmetry    = ''P3'' or ''P''{{overline|3}}
| unit cell   = a = 7.399(4) <br/>c = 10.311(15)&nbsp;[Å] <br/>V = 491.58 Å<sup>3</sup> 
| molweight   = 1076.12&nbsp;g/mol
| strunz      = 2.AC.10a
| color       = light creamy gray
| habit       = microscopic crystals
| twinning    = 
| cleavage    = 
| fracture    = 
| tenacity    = 
| mohs  = 4.5
| luster      = metallic
| refractive  = 
| opticalprop = weakly anisotropic in air; distinctly anisotropic in oil; no bireflectance; uniaxial
| pleochroism = no
| streak      = 
| gravity     = 
| density     = 10.96&nbsp;g/cm<sup>3</sup> 
| melt        = 
| fusibility  = 
| diagnostic  = 
| solubility  = 
| diaphaneity = opaque
| other       = non-radioactive
| references  = <ref> Cabri, L.J., and LaFlamme, J.H.G. (1974) Rhodium, Platinum, and Gold Alloys from the Stillwater Complex. Canadian Mineralogist, 12, 399-403.</ref><ref> CaBri, L.J., LaFlamme, J.H.G., Stewart, J.M., Rowland, J.F., and Chen, T.T. (1975) New data on some palladium arsenides and antimonides. Canadian Mineralogist, 13, 321-335.</ref><ref> Fleischer, M., Pabst, A., Mandarino, J.A., and Chao, G.Y. (1977) New Mineral Names. American Mineralogist, 62, 1060.</ref><ref> Hänninen, E., Törnroos, R., and Lahti, S.I. (1986) Stillwaterite and associated platinum group minerals from the Siikakämä layered mafic intrusion, northern Finland. ''[Lithos](/source/Lithos_(journal))'', 19, 87-93.</ref><ref> Jones, W.R., Peoples, J.W., and Howland, A.L. (1960) Igneous and Tectonic Structures of the Stillwater Complex, Montana. Geological Survey Bulletin, 1071-H, 281-333.</ref><ref> Klein, C., Dutrow, B. (2007) The 23rd Edition of the Manual of Mineral Science. 675 p. John Wiley & Sons, Hoboken, NJ.</ref><ref> Watkinson, D.H., and Dunning, G. (1979) Geology and Platinum-Group Mineralization, Lac-des-Iles Complex, Northwestern Ontario. Canadian Mineralogist, 17, 453-462. </ref><ref> [https://wwwn.cdc.gov/TSP/ToxFAQs/ToxFAQsLanding.aspx?id=19&tid=3 Centers for Disease Control and Prevention (CDC)] Accessed 19 November 2010.</ref><ref> [http://www.mindat.org/min-3787.html Mindat] Accessed 8 September 2010. </ref><ref> [http://webmineral.com/data/stillwaterite.shtml Webmineral] Accessed 24 September 2010.</ref> }}

'''Stillwaterite''' is a [palladium](/source/palladium) [arsenide mineral](/source/arsenide_mineral) which has a general formula of Pd<sub>8</sub>As<sub>3</sub>.  Stillwaterite was first discovered in the Banded and Upper zones of the [Stillwater igneous complex](/source/Stillwater_igneous_complex) in [Montana](/source/Montana), United States, and has been reported in the [Lac-des-Iles](/source/Lac-des-Iles) area of [Ontario](/source/Ontario), Canada.  Outside of North America, this rare mineral has been found in northern [Finland](/source/Finland).

==Symmetry==
Stillwaterite has [hexagonal](/source/Hexagonal_crystal_system) symmetry, meaning that it has four crystallographic axes: three are horizontal axes of equal length, and the fourth is a vertical axis of different length.

==Optical properties==
Because it is opaque, stillwaterite is most commonly viewed under reflected light, appearing light creamy gray in color.  It is weakly [anisotropic](/source/anisotropic) in air, displaying dark gray to brownish gray color.  In oil immersion, it shows distinct anisotropy with brownish black color and a blue to yellow-brown tinge.  Hexagonal minerals such as stillwaterite are referred to as [uniaxial crystal](/source/uniaxial_crystal)s because they have only one direction, along the optic axis, in which light is not reoriented.

==Significance==
Since its discovery in the mid-1970s, Stillwaterite has been studied to better understand the characteristics of complex mineral assemblages of gold, silicates, and other palladium arsenides with which it is associated. Minerals containing palladium can have economic significance, and are mined for use in industrial and commercial applications.

==References==
{{reflist}}

Category:Palladium minerals
Category:Arsenide minerals
Category:Trigonal minerals
Category:Minerals in space group 143
Category:Minerals in space group 147

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