Tsumebite is a rare

phosphate mineral Phosphate minerals contain the tetrahedrally coordinated phosphate (PO43−) anion along sometimes with arsenate (AsO43−) and vanadate (VO43−) substitutions, and chloride (Cl−), fluoride (F−), and hydroxide (OH−) anions that also fit i ...

named in 1912 after the locality where it was first found, the

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

in Namibia, well known to mineral collectors for the wide range of minerals found there. Tsumebite is a compound

phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phospho ...

and sulfate of

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 ...

and

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

, with

hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...

, formula . There is a similar mineral called arsentsumebite, where the

group is replaced by the arsenate group , giving the formula . Both minerals are members of the brackebuschite group.

The brackebuschite group

The minerals in the brackebuschite group have the general formula and crystallise in the

monoclinic system In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic s ...

, space group P2₁/m. The group includes: * brackebuschite * arsenbrackebuschite * gamagarite * goedkenite * bearthite *tsumebite * arsentsumebite *

vauquelinite Vauquelinite is a complex mineral with the formula Cu Pb2( Cr O4)( PO4)(O H) making it a combined chromate and phosphate of copper and lead. It forms a series with the arsenate mineral fornacite. It was first described in 1818 in the Beryozovs ...

* fornacite * molybdofornacite

Structure

The structure of the brackebuschite group minerals is composed of B-(O,OH)₆ octahedra, two non-equivalent TO₄

tetrahedra In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the o ...

, TO₄(1) and TO₄(2), and two different irregular polyhedra of large cations. B and T represent different elements in different members of the group. Chains formed from the B octahedra link through the

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

s of TO₄(2) tetrahedra, while the large cation polyhedra form double chains parallel to the b crystal axis through edge sharing with TO₄(1) tetrahedra. The result is a tight three-dimensional structure. In tsumebite

ions occupy the B sites, and

phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...

and

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...

occupy the T sites.

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 ...

is the large cation.

Unit cell

Tsumebite belongs to the

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic s ...

crystal class 2/m, meaning that it has one 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.

perpendicular to 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 ...

. The space group is P 2₁/m, meaning that the crystal lattice is a primitive lattice, with structural elements only at the vertices of the unit cell. These structural elements are made up of two formula units (Z = 2).
Unit cell parameters are a = 8.69 Å, b = 5.78 Å, c = 7.86 Å, β = 111.87° or a = 8.70 Å, b = 5.80 Å, c = 7.85 Å, β = 111.5°.

Optical properties

Tsumebite is an emerald-green color, transparent and green in transmitted light, with a green streak and an adamantine (diamond-like) to vitreous (glassy) luster. It is biaxial (+) with refractive indices N_x = 1.885 to 1.900, N_y = 1.920 and N_z = 1.942 to 1.956. It is faintly

pleochroic Pleochroism (from Greek πλέων, ''pléōn'', "more" and χρῶμα, ''khrôma'', "color") is an optical phenomenon in which a substance has different colors when observed at different angles, especially with polarized light. Backgroun ...

with X = Y = very pale blue to colorless and Z = robin's-egg-blue.

Physical properties

The mineral typically occurs as crusts of intergrown crystals on

matrix Matrix most commonly refers to: * ''The Matrix'' (franchise), an American media franchise ** ''The Matrix'', a 1999 science-fiction action film ** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchis ...

. Cleavage is absent, but twinning is almost universal, and twins may be multiple, with serrated re-entrants. It is brittle, with an uneven

fracture Fracture is the separation of an object or material into two or more pieces under the action of stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displa ...

hardness In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard ...

and

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 ...

6.13. It is readily soluble 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 ...

HCl and slowly soluble in

nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...

HNO₃. It is not

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...

Environment

Tsumebite 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 oxidised zone 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 lead-copper deposits, with other lead-bearing phosphates and sulfates. Associated minerals include

azurite Azurite is a soft, deep-blue copper mineral produced by weathering of copper ore deposits. During the early 19th century, it was also known as chessylite, after the Type locality (geology), type locality at Chessy, Rhône, Chessy-les-Mines near ...

, smithsonite,

malachite Malachite is a copper carbonate hydroxide mineral, with the formula Cu2CO3(OH)2. This opaque, green-banded mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses, in fractures ...

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 ...

, mimetite,

wulfenite Wulfenite is a lead molybdate mineral with the formula Pb Mo O4. It can be most often found as thin tabular crystals with a bright orange-red to yellow-orange color, sometimes brown, although the color can be highly variable. In its yellow form ...

and

olivenite Olivenite is a copper arsenate mineral, formula Cu2 As O4O H. It crystallizes in the monoclinic system (pseudo-orthorhombic), and is sometimes found in small brilliant crystals of simple prismatic habit terminated by domal faces. More commonly ...

. The type locality is the

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

, Tsumeb, Otjikoto Region, Namibia. The Handbook of Mineralogy states that the type material was destroyed by bombing, but does not indicate when or where. Tsumebite occurs at

Morenci, Arizona Morenci is a census-designated place (CDP) and company town in Greenlee County, Arizona, United States, and was founded by the Detroit Copper Mining Company of Arizona. The population was 2000 at the 2000 census and 1,489 at the 2010 census. Th ...

, predominantly as twinned crystals associated with

and the

hyalite Hyalite is a transparent form of opal with a glassy lustre. It may exhibit an internal play of colors if natural inclusions are present. It is also called Muller's glass, water opal, and jalite. Müller's glass is named after its discoverer, Fra ...

variety of

opal Opal is a hydrated amorphous form of silica (SiO2·''n''H2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Due to its amorphous property, it is classified as a mineraloid, unlike crystalline forms ...

. At

Broken Hill, New South Wales Broken Hill is an inland mining city in the far west of outback New South Wales, Australia. It is near the border with South Australia on the crossing of the Barrier Highway (A32) and the Silver City Highway (B79), in the Barrier Range. It is ...

, Australia, tsumebite has been found as lustrous pale blue to bluish green crystals. It usually occurs with yellow crusts of

corkite Corkite is a phosphate mineral in the beudantite subgroup of the alunite group. Corkite is the phosphate analogue of beudantite and with it, a complete solid solution range exists. Corkite will also form a solid solution with kintoreite. Cork ...

- hinsdalite, colorless to white

pyromorphite Pyromorphite is a mineral species composed of lead chlorophosphate: Pb5( P O4)3 Cl, sometimes occurring in sufficient abundance to be mined as an ore of lead. Crystals are common, and have the form of a hexagonal prism terminated by the basal pla ...

needles and sprays of pale greyish green

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 ...

ian

libethenite Libethenite is a rare copper phosphate hydroxide mineral. It forms striking, dark green orthorhombic crystals. It was discovered in 1823 in Ľubietová, Slovakia and is named after the German name of that locality (''Libethen''). Libethenite has a ...

. Less commonly found with scholzite and torbernite.Australian Journal of Mineralogy (1997) 3-1:53

References

* LaForge (1938) American Mineralogist: 23: 772

External links

*Jmol: http://rruff.geo.arizona.edu/AMS/viewJmol.php?id=14449 {{Commons category, Tsumebite Phosphate minerals Lead minerals Copper(II) minerals Monoclinic minerals Minerals in space group 11