Tsumcorite

{{Short description|Rare hydrated lead arsenate mineral}} {{Infobox mineral | name = Tsumcorite | category = Arsenate minerals | boxwidth = | boxbgcolor = | image = Tsumcorite-160209.jpg | caption = Tsumcorite from the Tsumeb Mine, Namibia | formula = PbZnFe2+(AsO4)2.H2O | IMAsymbol = Tmc<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 = 624.29 g/mol | strunz = 8.CG.15 | dana = 40.02.09.01 | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = ''C2/m'' (no. 12) | unit cell = a = 9.124 Å, b = 6.329 Å c = 7.577 Å; β = 115.3°; Z = 2 | color = Yellow-brown, red-brown, orange | habit = Radiating, fibrous crusts | twinning = Common, on an unknown law | cleavage = Good on {001} | fracture = | tenacity = | mohs = {{frac|4|1|2}} | luster = Vitreous | refractive = nα = 1.87–1.91 nβ = 1.89–1.93 nγ = 1.92–1.96 | opticalprop = Biaxial | birefringence = | pleochroism = Weak, yellow to yellow-green | 2V = 67–83.5° | streak = Yellow | gravity = 5.2 | melt = | fusibility = | diagnostic = | solubility = Dissolves in HCl | diaphaneity = Translucent | other = | references = <ref name=Dana>Gaines et al (1997) Dana’s New Mineralogy Eighth Edition. Wiley</ref><ref name=Mindat>[http://www.mindat.org/min-4039.html Mindat.org]</ref><ref name=Webmin>[http://www.webmineral.com/data/Tsumcorite.shtml Webmineral data]</ref><ref name=HOM>[http://www.handbookofmineralogy.org Handbook of Mineralogy]</ref><ref name=AM57>Fleischer M (1972) New mineral names, American Mineralogist 57, 1558, being a summary of Geier, Kautz and Muller (1971) Neues Jahrbuch für Mineralogie (Monatshefte) 1971: 304–309</ref><ref>{{cite journal |last1=Tillmanns |first1=E. |last2=Gebert |first2=W. |title=The crystal structure of tsumcorite, a new mineral from the Tsumeb mine, S. W. Africa |journal=Acta Crystallographica Section B: Structural Crystallography and Crystal Chemistry |date=1 December 1973 |volume=29 |issue=12 |pages=2789–2794 |doi=10.1107/S0567740873007545|bibcode=1973AcCrB..29.2789T }}</ref>}} '''Tsumcorite''' is a rare hydrated lead arsenate mineral that was discovered in 1971, and reported by Geier, Kautz and Muller.<ref name = AM57/> It was named after the '''TSUM'''eb '''COR'''poration mine at Tsumeb, in Namibia, in recognition of the Corporation's support for mineralogical investigations of the orebody at its Mineral Research Laboratory.<ref name=HOM/>

== Unit cell == Tsumcorite belongs to the monoclinic crystal class 2/m, which means that it has a twofold axis of symmetry along the b axis and a mirror plane perpendicular to this, in the plane containing the a and c axes. The a and c axes are inclined to each other at angle β = 115.3°. The unit cell parameters are a = 9.124 Å to 9.131 Å, b = 6.326 Å to 6.329 Å and c = 7.577 Å to 7.583 Å.<ref name=Dana/><ref name = Mindat/><ref name=Webmin/><ref name=AM57/> There are two formula units per unit cell (Z = 2), and the space group is C2/m, meaning that the cell is a C-face centred lattice, with lattice points in the center of the C face as well as at the corners of the cell.<ref name=Ott>Crystallography (1993) Walter Borchardt-Ott, Springer Verlag</ref> The structure is related to the brackebushite group structure.<ref name=Dana/>

== Mineral series == Tsumcorite belongs to the helmutwinklerite group,<ref name = Dana/> whose members are *tsumcorite PbZnFe2+(AsO4)2.H2O *helmutwinklerite PbZn2(AsO4)2.2H2O *thometzekite PbCu2+2(AsO4)2.2H2O *mawbyite PbFe3+2(AsO4)2(OH)2 Tsumcorite forms a series with helmutwinklerite as Zn replaces the Fe2+, with thometzekite as Cu replaces the Zn and Fe2+,<ref name=Dana/><ref name=Webmin/> and also with mawbyite.<ref name=AJM>Australian Journal of Mineralogy (1997) 3-1:62</ref>

== Crystal habit and properties == Crystals are prismatic, elongated along the b axis, or wedge-shaped. They occur in radiating sheaves and spherulites, and as fibrous crusts or earthy and powdery material.<ref name=HOM/> Cleavage is good perpendicular to the c axis,<ref name=HOM/> and twinning is common.<ref name=HOM/>

Tsumcorite is yellow-brown, red-brown or orange in color, and it is one of the few minerals that have a yellow streak (orpiment and crocoite are two others). It is translucent, with a vitreous luster, and dichroic yellow to yellow-green.<ref name=Dana/><ref name=AM57/> The optical class is biaxial and the refractive indices are approximately equal to 1.90.<ref name=Dana/><ref name=Webmin/><ref name=AM57/>

The mineral is moderately hard, with a Mohs hardness of {{frac|4|1|2}}, between fluorite and apatite,<ref name=Dana/><ref name = Mindat/><ref name=Webmin/><ref name=HOM/> and quite heavy, due to the lead content, with specific gravity 5.2, which is more than baryte but less than cerussite. It dissolves in hydrochloric acid<ref name=Dana/><ref name=AM57/> and it is not radioactive.<ref name=Webmin/>

== Occurrence and associations == Tsumcorite is a rare secondary mineral in the oxidized zone of some arsenic-bearing hydrothermal lead-zinc deposits.<ref name=Dana/><ref name=HOM/><ref name=AM57/>

The type locality is the Tsumeb Mine, Tsumeb, Otjikoto Region, Namibia, where it is associated with willemite, smithsonite, mimetite, scorodite, anglesite, arseniosiderite, beaverite, beudantite, carminite, ludlockite, o'danielite, zincroselite, stranskiite and leiteite.<ref name=HOM/> At the Puttapa Mine in Australia it occurs with adamite, mimetite, smithsonite, goethite and quartz.<ref name=HOM/> At the Kintore Open Cut, Broken Hill, Australia it occurs with segnitite, beudantite, carminite and mawbyite.<ref name=AJM/>

== References == {{commons category| Tsumcorite}} {{Reflist}}

Category:Arsenate minerals Category:Lead minerals Category:Zinc minerals Category:Iron(II) minerals Category:Monoclinic minerals Category:Minerals in space group 12 Category:Minerals described in 1971