{{Short description|Sulfate mineral}} {{Infobox mineral | name = Leightonite | category = Sulfate minerals | image = Leightonite-120493.jpg | imagesize = 260px | caption = | formula = K<sub>2</sub>Ca<sub>2</sub>Cu(SO<sub>4</sub>)<sub>4</sub>•2H<sub>2</sub>O | IMAsymbol = Lgh<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 = | strunz = 7.CC.70 | system = Monoclinic | class = Prismatic (2/m) <br/><small>(same H-M symbol)</small> | symmetry = ''C2/c'' | unit cell = | color = Pale blue, greenish-blue; pale blue in transmitted light. | habit = Lathlike crystals, flattened, elongated or equant; pseudo-orthorhombic | twinning = Lamellar twinning on (100) and (010) produces pseudo-orthorhombic symmetry | cleavage = None observed | fracture = | tenacity = | mohs = 3 | luster = Vitreous | refractive = n<sub>α</sub> = 1.578 n<sub>β</sub> = 1.587 n<sub>γ</sub> = 1.595 | opticalprop = Biaxial (-) | birefringence = δ = 0.017 | pleochroism= | streak= | gravity = 2.95 | density = | melt= | fusibility= | diagnostic= | solubility= | diaphaneity = Transparent, translucent | other= | references = <ref name=Palache>Palache, C. (1938) Leightonite, a new sulphate of copper from Chile. American Mineralogist, 23, 34-37.</ref><ref name=Mindat/> }} '''Leightonite''' is a rare sulfate mineral with formula of K<sub>2</sub>Ca<sub>2</sub>Cu(SO<sub>4</sub>)<sub>4</sub>•2H<sub>2</sub>O.<ref name=Mindat/>
==Crystal class== Leightonite forms flattened to elongated bladed crystals of variously interpreted crystal structure. Its crystal system is reported as triclinic morphologically, but also as pseudo-orthorhombic due to intricate lamellar twinning that mimics orthorhombic symmetry.<ref name=Palache/><ref name=Mindat/> Because it is triclinic, the crystal is represented by a system of three unequal vectors with corresponding unequal angles between them.
==Optical class== Leightonite is anisotropic, meaning it has more than one refractive index, in this case three as it is biaxial. The mineral can split polarized light into two rays with different direction and velocity, resulting in the appearance of interference colors when recombined and viewed under polarized light.
==Discovery and occurrence== It was first described in 1938 for an occurrence in the Chuquicamata Mine, Colama, El Loa Province, Antofagasta Region, Chile,<ref name=Mindat>[http://www.mindat.org/min-2369.html Mindat.org]</ref> and named in honor of Tomas Leighton Donoso (1896–1967), Professor of Mineralogy at the University of Santiago, Chile.<ref name=Palache/><ref name=HBM/>
It occurs in alkali oxidized zones of copper deposits and is associated with natrochalcite, blodite, atacamite, bellingerite, kröhnkite, gypsum and quartz in the discovery location at Chuquicamata, Chile, along with chalcanthite, anhydrite and lammerite in Tsumeb, Namibia.<ref name=HBM>[http://rruff.geo.arizona.edu/doclib/hom/leightonite.pdf Handbook of Mineralogy]</ref> It has also been reported from the Schwaz area of North Tyrol, Austria, and the Visdalen Soapstone Quarry, Lom, Norway.<ref name=Mindat/>
At the mining site of Chuquicamata, Chile, Leightonite is not found in rich ore; rather it only appears in borderland material within {{convert|50|m|abbr=on}} of the surface, acting as a cement between rock fragments as it fills in cracks and cross-fiber veins in surfaces as a network of crystals.<ref name=Palache/> Although a hydrous sulfate of copper, it is not a major source of the element. Because of its rare nature, it is valued by mineral collectors.
==References== {{reflist}}
Category:Potassium minerals Category:Calcium minerals Category:Copper(II) minerals Category:Sulfate minerals Category:Monoclinic minerals Category:Minerals in space group 15 Category:Minerals described in 1938