Tsumcorite

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Tsumcorite
Tsumcorite-160209.jpg
Tsumcorite from the Tsumeb Mine, Namibia
General
CategoryArsenate minerals
Formula
(repeating unit)		PbZnFe2+(AsO4)2.H2O
IMA symbolTmc[1]
Strunz classification8.CG.15
Dana classification40.02.09.01
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupC2/m (no. 12)
Unit cella = 9.124 Å, b = 6.329 Å
c = 7.577 Å; β = 115.3°; Z = 2
Identification
Formula mass624.29 g/mol
ColorYellow-brown, red-brown, orange
Crystal habitRadiating, fibrous crusts
TwinningCommon, on an unknown law
CleavageGood on {001}
Mohs scale hardness4+1⁄2
LusterVitreous
StreakYellow
DiaphaneityTranslucent
Specific gravity5.2
Optical propertiesBiaxial
Refractive indexnα = 1.87–1.91 nβ = 1.89–1.93 nγ = 1.92–1.96
PleochroismWeak, yellow to yellow-green
2V angle67–83.5°
SolubilityDissolves in HCl
References[2][3][4][5][6][7]

Tsumcorite is a rare hydrated lead arsenate mineral that was discovered in 1971, and reported by Geier, Kautz and Muller.[6] It was named after the TSUMeb CORporation mine at Tsumeb, in Namibia, in recognition of the Corporation's support for mineralogical investigations of the orebody at its Mineral Research Laboratory.[5]

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.[2][3][4][6] 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.[8] The structure is related to the group structure.[2]

Mineral series[]

Tsumcorite belongs to the helmutwinklerite group,[2] 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+,[2][4] and also with mawbyite.[9]

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.[5] Cleavage is good perpendicular to the c axis,[5] and twinning is common.[5]

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.[2][6] The optical class is biaxial and the refractive indices are approximately equal to 1.90.[2][4][6]

The mineral is moderately hard, with a Mohs hardness of 4+1⁄2, between fluorite and apatite,[2][3][4][5] 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[2][6] and it is not radioactive.[4]

Occurrence and associations[]

Tsumcorite is a rare secondary mineral in the oxidized zone of some arsenic-bearing hydrothermal lead-zinc deposits.[2][5][6]

The type locality is the Tsumeb Mine, Tsumeb, Otjikoto Region, Namibia, where it is associated with willemite, smithsonite, mimetite, scorodite, anglesite, arseniosiderite, , beudantite, carminite, , , , and .[5] At the Puttapa Mine in Australia it occurs with adamite, mimetite, smithsonite, goethite and quartz.[5] At the Kintore Open Cut, Broken Hill, Australia it occurs with segnitite, beudantite, carminite and .[9]

References[]

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b c d e f g h i j Gaines et al (1997) Dana’s New Mineralogy Eighth Edition. Wiley
  3. ^ a b c Mindat.org
  4. ^ a b c d e f Webmineral data
  5. ^ a b c d e f g h i Handbook of Mineralogy
  6. ^ a b c d e f g Fleischer M (1972) New mineral names, American Mineralogist 57, 1558, being a summary of Geier, Kautz and Muller (1971) Neues Jahrbuch fur Mineralogie (Monatshefte) 1971: 304–309
  7. ^ Tillmanns, E.; Gebert, W. (1 December 1973). "The crystal structure of tsumcorite, a new mineral from the Tsumeb mine, S. W. Africa". Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry. 29 (12): 2789–2794. doi:10.1107/S0567740873007545.
  8. ^ Crystallography (1993) Walter Borchardt-Ott, Springer Verlag
  9. ^ a b Australian Journal of Mineralogy (1997) 3-1:62
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