Tsumcorite is a rare hydrated

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

arsenate The arsenate ion is . An arsenate (compound) is any compound that contains this ion. Arsenates are salts or esters of arsenic acid. The arsenic atom in arsenate has a valency of 5 and is also known as pentavalent arsenic or As(V). Arsenate resem ...

mineral that was discovered in 1971, and reported by Geier, Kautz and Muller. It was named after the TSUMeb CORporation mine at

Tsumeb , nickname = , settlement_type = City , motto = ''Glück Auf'' (German language, German for ''Good luck'') , image_skyline = Welcome to tsumeb.jpg , imagesize = , image_caption ...

, in Namibia, in recognition of the Corporation's support for mineralogical investigations of the orebody at its Mineral Research Laboratory.

Unit cell

Tsumcorite belongs to the monoclinic crystal class 2/m, which means that it has a twofold

axis of symmetry Axial symmetry is symmetry around an axis; an object is axially symmetric if its appearance is unchanged if rotated around an axis.

along the b

axis An axis (plural ''axes'') is an imaginary line around which an object rotates or is symmetrical. Axis may also refer to: Mathematics * Axis of rotation: see rotation around a fixed axis *Axis (mathematics), a designator for a Cartesian-coordinate ...

and a

mirror plane In mathematics, a reflection (also spelled reflexion) is a mapping from a Euclidean space to itself that is an isometry with a hyperplane as a set of fixed points; this set is called the axis (in dimension 2) or plane (in dimension 3) of refle ...

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 In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessaril ...

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. There are two formula units per unit cell (Z = 2), and the

space group In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it unchan ...

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.Crystallography (1993) Walter Borchardt-Ott, Springer Verlag The structure is related to the brackebushite group structure.

Mineral series

Tsumcorite belongs to the helmutwinklerite group, 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⁺, and also with mawbyite.Australian Journal of Mineralogy (1997) 3-1:62

Crystal habit and properties

Crystals are

prismatic An optical prism is a transparent optical element with flat, polished surfaces that are designed to refract light. At least one surface must be angled — elements with two parallel surfaces are ''not'' prisms. The most familiar type of optical ...

, elongated along the b axis, or wedge-shaped. They occur in radiating sheaves and spherulites, and as fibrous crusts or earthy and powdery material. Cleavage is good perpendicular to the c axis, and twinning is common. Tsumcorite is yellow-brown, red-brown or orange in color, and it is one of the few minerals that have a yellow streak (

orpiment Orpiment is a deep-colored, orange-yellow arsenic sulfide mineral with formula . It is found in volcanic fumaroles, low-temperature hydrothermal veins, and hot springs and is formed both by sublimation and as a byproduct of the decay of another a ...

and

crocoite Crocoite is a mineral consisting of lead chromate, Pb Cr O4, and crystallizing in the monoclinic crystal system. It is identical in composition with the artificial product chrome yellow used as a paint pigment. Description Crocoite is commonl ...

are two others). It is translucent, with a vitreous luster, and

dichroic In optics, a dichroic material is either one which causes visible light to be split up into distinct beams of different wavelengths (colours) (not to be confused with dispersion), or one in which light rays having different polarizations are abs ...

yellow to yellow-green. The optical class is biaxial and the

refractive indices In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...

are approximately equal to 1.90. The mineral is moderately hard, with a

Mohs hardness The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by th ...

of , between

fluorite Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. The Mohs sca ...

and

apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ions, respectively, in the crystal. The formula of the admixture of the three most common e ...

, and quite heavy, due to the lead content, with

specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water (molecule), wa ...

5.2, which is more than

baryte Baryte, barite or barytes ( or ) is a mineral consisting of barium sulfate ( Ba S O4). Baryte is generally white or colorless, and is the main source of the element barium. The ''baryte group'' consists of baryte, celestine (strontium sulfate), ...

but less than

cerussite Cerussite (also known as lead carbonate or white lead ore) is a mineral consisting of lead carbonate (PbCO3), and is an important ore of lead. The name is from the Latin ''cerussa'', white lead. ''Cerussa nativa'' was mentioned by Conrad Gessner ...

. It dissolves in

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid Acid strength is the tendency of an acid, symbol ...

and it is not radioactive.

Occurrence and associations

Tsumcorite is a rare

secondary mineral A primary mineral is any mineral formed during the original crystallization of the host igneous primary rock and includes the essential mineral(s) used to classify the rock along with any accessory minerals. In ore deposit geology, hypogene processe ...

in the

oxidized zone Gossan (eiserner hut or eisenhut) is intensely oxidized, weathered or decomposed rock, usually the upper and exposed part of an ore deposit or mineral vein. In the ''classic'' gossan or iron cap all that remains is iron oxides and quartz, often i ...

of some

arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but ...

-bearing

hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...

deposits. The type locality is the

Tsumeb , nickname = , settlement_type = City , motto = ''Glück Auf'' (German language, German for ''Good luck'') , image_skyline = Welcome to tsumeb.jpg , imagesize = , image_caption ...

Mine, Tsumeb, Otjikoto Region, Namibia, where it is associated with

willemite Willemite is a zinc silicate mineral () and a minor ore of zinc. It is highly fluorescent (green) under shortwave ultraviolet light. It occurs in a variety of colors in daylight, in fibrous masses and apple-green gemmy masses. Troostite is a vari ...

smithsonite Smithsonite, also known as zinc spar, is the mineral form of zinc carbonate ( Zn CO3). Historically, smithsonite was identified with hemimorphite before it was realized that they were two different minerals. The two minerals are very similar in app ...

mimetite Mimetite is a lead arsenate chloride mineral (Pb5(AsO4)3Cl) which forms as a secondary mineral in lead deposits, usually by the oxidation of galena and arsenopyrite. The name derives from the Greek Μιμητής ''mimetes'', meaning "imitator" a ...

scorodite Scorodite is a common hydrated iron arsenate mineral, with the chemical formula FeAsO4·2H2O. It is found in hydrothermal deposits and as a secondary mineral in gossans worldwide. Scorodite weathers to limonite. Scorodite was discovered in the S ...

anglesite Anglesite is a lead sulfate mineral with the chemical formula PbSO4. It occurs as an oxidation product of primary lead sulfide ore, galena. Anglesite occurs as prismatic orthorhombic crystals and earthy masses, and is isomorphous with barite and ...

arseniosiderite Arseniosiderite is a rare arsenate mineral formed by the oxidation of other arsenic-containing minerals, such as scorodite or arsenopyrite Arsenopyrite ( IMA symbol: Apy) is an iron arsenic sulfide (FeAsS). It is a hard ( Mohs 5.5-6) metallic ...

, beaverite,

beudantite Beudandite is a secondary mineral occurring in the oxidized zones of polymetallic deposits. It is a lead, iron, arsenate, sulfate with endmember formula: PbFe3(OH)6SO4AsO4. Beudantite is in a subgroup of the alunite group. It is the arsenate an ...

carminite Carminite (PbFe3+2(AsO4)2(OH)2) is an anhydrous arsenate mineral containing hydroxyl. It is a rare secondary mineral that is structurally related to palermoite (Li2SrAl4(PO4)4(OH)4). Sewardite (CaFe3+2(AsO4)2(OH)2) is an analogue of carmin ...

, ludlockite, o'danielite, zincroselite, stranskiite and leiteite. At the Puttapa Mine in Australia it occurs with

adamite Adamite is a zinc arsenate hydroxide mineral, Zn2 As O4O H. It is a mineral that typically occurs in the oxidized or weathered zone above zinc ore occurrences. Pure adamite is colorless, but usually it possess yellow color due to Fe compounds a ...

goethite Goethite (, ) is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the "α" polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient t ...

and

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...

. At the Kintore Open Cut, Broken Hill, Australia it occurs with

segnitite } Segnitite is a lead iron(III) arsenate mineral. Segnitite was first found in the Broken Hill ore deposit in Broken Hill, New South Wales, Australia. In 1991, segnitite was approved as a new mineral. Segnitite has since been found worldwide nea ...

and

mawbyite Mawbyite is a lead iron zinc arsenate that was named in honor of Maurice Alan Edgar Mawby. It has been approved by the IMA in 1988, and was published just a year after being described by Pring. Mawbyite is a member of the tsumcorite group, the m ...

References

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