View source for Langite

{{Infobox mineral
| name = Langite
| category = Copper minerals
| boxwidth = 24
| boxbgcolor =
| image = Langite-120989.jpg
| imagesize   = 260px
| caption = Langite from Podlipa and Reinera Mines, Slovakia
| formula = Cu<sub>4</sub>(SO<sub>4</sub>)(OH)<sub>6</sub>·2H<sub>2</sub>O
| IMAsymbol   = Lgt<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>
| molweight = 488.32 g/mol
| strunz = 7.DD.10
| dana = 31.4.3.1
| system = [[Monoclinic]]
| class = Domatic (m) <br/><small>(same [[H-M symbol]])</small>
| symmetry = ''Pc''
| unit cell = a = 7.118, b = 6.031 <br/>c = 11.209&nbsp;[Å] <br/>β = 90.00–90.02°; Z&nbsp;=&nbsp;2
| color = Greenish blue, sky-blue to bluish green
| habit = Crystals scaly, or as crusts; earthy
| twinning = Common on {110}, typically repeated
| cleavage = {001} perfect, {010} distinct
| fracture = Uneven
| tenacity =
| mohs = 2.5 to 3
| luster = Vitreous, crusts silky
| refractive = n<sub>α</sub> = 1.708 n<sub>β</sub> = 1.760 n<sub>γ</sub> = 1.798 <ref name=Mindat/>
| opticalprop = Biaxial (−) r>v weak
| birefringence = δ = 0.090
| pleochroism = X = c = light yellowish green<br/>Y = b = blue-green<br/>Z = a = sky blue
| streak = Blue green
| gravity = 3.28<ref name=Dana/> 3.48 to 3.5<ref name=Mindat/> 3.5<ref name=Webmin/> 2.28 to 3.34<ref name=HOM/>
| density =
| melt =
| fusibility =
| diagnostic =
| solubility = Insoluble in water, easily soluble in dilute acids or NH<sub>4</sub>OH
| diaphaneity = Translucent
| other = May be altered to [[brochantite]].  Not radioactive
| references = <ref name=Mindat>[http://www.mindat.org/min-2322.html Mindat.org]</ref><ref name=Dana>Gaines et al (1997) Dana’s New Mineralogy Eighth Edition, Wiley</ref><ref name=Webmin>[http://www.webmineral.com/data/Langite.shtml Webmineral data]</ref><ref name=HOM>[http://rruff.geo.arizona.edu/doclib/hom/langite.pdf Handbook of Mineralogy]</ref> }}
'''Langite''' is a rare hydrated copper [[sulfate mineral]], with hydroxyl, found almost exclusively in [[Druse (geology)|druses]] of small crystals.  It is formed from the [[oxidation]] of [[copper sulfide]]s, and was first described in specimens from [[Cornwall]], United Kingdom.  It is [[Polymorphism (materials science)|dimorphous]] with [[wroewolfeite]]. Langite was discovered in 1864 and named after the physicist and crystallographer [[Viktor von Lang]] (1838–1921), who was Professor of Physics at the [[University of Vienna]], Austria.<ref name=Mindat/>
== Unit cell ==
Langite belongs to the [[monoclinic]] crystal class m, meaning that it has just one [[mirror plane]], and no [[Rotational symmetry|axes of rotational symmetry]]. The crystal is built up of identical [[Crystal structure|unit cells]] stacked together, with no space in between.  The unit cell for the monoclinic system has a base which is a [[rhombus]], with sides a and c inclined at angle β. The third side b is perpendicular to both a and c. For langite the angle β is very close to 90°, so the unit cell is almost brick-shaped (as for the [[orthorhombic]] system). Different sources give slightly different values for the unit cell parameters, but they all fall within the ranges a = 7.118 Å to 7.137 Å, b = 6.031 Å to 6.034 Å, c = 11.209 Å to 11.217 Å, β = 90.00 to 90.02°, Z (the number of formula units per unit cell) = 2.<ref name = Mindat/><ref name=Dana/><ref name=Webmin/><ref name=HOM/>
== Physical properties ==
Langite usually occurs as druses of small greenish-blue crystals which may be scaly or earthy.  It is translucent, with a vitreous to silky [[Lustre (mineralogy)|luster]] and a blue-green [[Streak (mineralogy)|streak]]. It has perfect [[Cleavage (crystal)|cleavage]] perpendicular to the c crystal axis, and distinct cleavage perpendicular to b. [[Crystal twinning|Twinning]] is common, and typically repeated to give snowflake or star shaped groupings.<ref name=Mindat/><ref name = HOM/> The mineral is soft, with [[Mohs scale of mineral hardness|hardness]] 2.5 to 3, a little less than that of calcite. [[Fracture (mineralogy)|Fracture]] is uneven, and [[specific gravity]] is in the range 3.28 to 3.50,<ref name = Mindat/><ref name=Dana/><ref name=Webmin/><ref name=HOM/> a little less than that of diamond.
== Optical properties ==
Langite is biaxial (−). Since it is monoclinic, it has three different refractive indices, corresponding to the three crystallographic directions. All the refractive indices are in the range 1.64 to 1.80, which is comparatively large, almost as high as garnet. Different sources give these values:
:N<sub>x</sub> = 1.641, N<sub>y</sub> = 1.690, N<sub>z</sub> = 1.712<ref name=Dana/>
:N<sub>x</sub> = 1.708, N<sub>y</sub> = 1.760, N<sub>z</sub> = 1.798<ref name=Mindat/><ref name=Webmin/>
:N<sub>x</sub> = 1.641 to 1.654, N<sub>y</sub> = 1.690 to 1.713, N<sub>z</sub> = 1.705 to 1.722<ref name=HOM/>
:N<sub>x</sub> = 1.641, N<sub>y</sub> = 1.690, N<sub>z</sub> = 1.705 to 1.712<ref name=AM49>American Mineralogist (1964) 49:1143</ref>
The mineral is [[Pleochroism|pleochroic]], with X light yellowish green, Y blue-green and Z sky blue.<ref name=Mindat/>
== Occurrence ==
Langite is an uncommon but widespread secondary mineral in the oxidised zone of copper sulfide deposits, which may be of post-mine formation. It is associated with [[wroewolfeite]], [[posnjakite]], [[serpierite]], [[devilline]], [[chalcophyllite]], [[connellite]], [[brochantite]], [[malachite]] and [[gypsum]].<ref name=HOM/>
There are two [[type locality (geology)|type localities]] for langite, [[Fowey Consols]], [[Tywardreath]], Par Area, [[St Austell]] District, and [[St Just in Penwith|St Just]], St Just District, both in Cornwall, England. The type material is conserved at the [[Naturhistorisches Museum|Natural History Museum]], Vienna, Austria, reference A.a.4353.
Other reported occurrences include:
* With [[serpierite]] coating the bed of a water course affected by [[acid mine drainage]] at the Lloyd Copper Mine at [[Burraga|Burraga, New South Wales]], Australia<ref name=AU10>Australian Journal of Mineralogy (2004) 10-1:3</ref>
* Intergrown with [[ktenasite]] forming fibrous and botryoidal crusts and coatings less than 0.1&nbsp;mm thick, at the Kintore Open Cut, [[Broken Hill, New South Wales]], Australia<ref name=AU3>Australian Journal of Mineralogy (1997) 3-1:43</ref>
* Associated with a new mineral [[mallestigite]], reported in 2004, near [[Carinthia (state)|Carinthia]], Austria, on the dump of a copper-lead-zinc mine. The mallestigite formed in fractures during weathering of primary [[galena]] and [[tetrahedrite]]. Other associated minerals were [[anglesite]], [[brochantite]], [[linarite]] and [[schultenite]]<ref name=MinRec>The Mineralogical Record (2004) 35-4:357</ref>
* At Silver Gill, Caldbeck Fells, [[Cumbria]], England, partly altered to [[brochantite]], Cu<sub>4</sub>SO<sub>4</sub>(OH)<sub>6</sub><ref name=MM>Mines & Minerals (2005)25:6</ref>
* As microcrystals in small vugs in [[prehnite]]-[[quartz]] vein sections at the Clark Mine, [[Keweenaw Peninsula]], Michigan, US<ref name=R&M>Rocks & Minerals (2009) 84-4:321</ref>
== References ==
{{Reflist}}
== External links ==
{{Portal|Cornwall}}
*Jmol: http://rruff.geo.arizona.edu/AMS/viewJmol.php?id=09777
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[[Category:Copper(II) minerals]]
[[Category:Sulfate minerals]]
[[Category:Monoclinic minerals]]
[[Category:Minerals in space group 7]]