Plumbogummite is a rare secondary lead

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

, belonging to the

alunite Alunite is a hydroxylated aluminium potassium sulfate mineral, formula potassium, Kaluminium, Al3(sulfur, Soxygen, O4)2(Ohydrogen, H)6. It was first observed in the 15th century at Tolfa, near Rome, where it was mined for the manufacture of alum ...

supergroup of minerals,

crandallite Crandallite is a calcium aluminium basic phosphate mineral. It has ideal formula . Crandallite was named after Milan L. Crandall Jr, who worked for Knight Syndicate. This mineral is found in laterite and in alteration products of phosphate rich p ...

subgroup. Some other members of this subgroup are: * Crandallite, CaAl₃(PO₄)₂(OH)₅·H₂O, where calcium replaces lead * Goyazite, SrAl₃(PO₄)₂(OH)₅·H₂O, where strontium replaces lead * Philipsbornite, PbAl₃(AsO₄)₂(OH)₅·H₂O, where the

arsenate The arsenate is an ion with the chemical formula . Bonding in arsenate consists of a central arsenic atom, with oxidation state +5, double bonded to one oxygen atom and single bonded to a further three oxygen atoms. The four oxygen atoms orien ...

group AsO₄ replaces the phosphate group PO₄ Plumbogummite was discovered in 1819 and named in 1832 from the Latin "plumbum" for lead, and "gummi" for gum, in allusion to its lead content and appearance, which at times resembles coatings of gum.

Unit cell

Plumbogummite crystallizes in space group Rm. The reported

lattice parameter A lattice constant or lattice parameter is one of the physical dimensions and angles that determine the geometry of the unit cells in a crystal lattice, and is proportional to the distance between atoms in the crystal. A simple cubic crystal has ...

s (the lengths of the sides of the unit cell) vary in detail according to the source, but all agree that normal plumbogummite has "a" close to 7 Å and "c" close to 17 Å, with Z=3. Various reported values of "a" and "c"are: :a = 7.01 Å, 7.017 Å, 7.018 Å, 7.033 Å :c = 16.71Å, 16.75 Å, 16.784 Å, 16.789 Å Mills ''et al.'' investigated a

gallium Gallium is a chemical element; it has Chemical symbol, symbol Ga and atomic number 31. Discovered by the French chemist Paul-Émile Lecoq de Boisbaudran in 1875, elemental gallium is a soft, silvery metal at standard temperature and pressure. ...

-rich sample of plumbogummite from

Tsumeb Tsumeb (; ) is a city of around 35,000 inhabitants and the largest town in the Oshikoto Region, Oshikoto region in northern Namibia. Tsumeb, since its founding in 1905, has been primarily a mining town. The town is the site of a deep mine (the ...

, Namibia, and found larger cell parameters, with a = 7.0752 Å and c = 16.818 Å.

Structure

The basic structural units of plumbogummite are PO₄

tetrahedra In geometry, a tetrahedron (: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular Face (geometry), faces, six straight Edge (geometry), edges, and four vertex (geometry), vertices. The tet ...

, with phosphorus atoms (P) at the center and oxygen atoms (O) at the corners, together with AlO₆ octahedra, aluminium atoms (Al) at the center and oxygen atoms at the corners. The tetrahedra and octahedra combine by sharing corners, to form composite layers. Lead atoms (Pb) occupy sites between the layers.

Environment

Plumbogummite is found in the oxidized zones of lead-bearing deposits. It commonly occurs as

botryoidal A botryoidal ( ) texture or mineral habit, is one in which the mineral has an external form composed of many rounded segments, named for the Ancient Greek (), meaning "a bunch of grapes".Adjective form: ''botruoeidēs'' This is a common form f ...

, kidney shaped, stalactitic or globular crusts or masses, frequently with a concentric structure; rare crystals have a

hexagonal In geometry, a hexagon (from Greek , , meaning "six", and , , meaning "corner, angle") is a six-sided polygon. The total of the internal angles of any simple (non-self-intersecting) hexagon is 720°. Regular hexagon A regular hexagon is d ...

outline.

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 p ...

and

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), ...

are commonly associated minerals, and plumbogummite may be

pseudomorph In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form (crystal system), resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced b ...

ic after them. Other associated minerals include

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

duftite Duftite is a relatively common arsenate mineral with the formula CuPb(AsO4)(OH), related to conichalcite. It is green and often forms botryoidal aggregates. It is a member of the adelite-descloizite Group, Conichalcite-Duftite Series. Duftite and ...

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

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 ...

and

wulfenite Wulfenite is a lead molybdate mineral with the formula Pb Mo O4. It often occurs 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 it is some ...

Occurrence

The type locality is Huelgoat, Finistère, Brittany, France, and the

type material In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...

is stored in the Natural History Museum, Paris, France. Plumbogummite has been found in the Central Cobar Mines, New South Wales, AustraliaAustralian Journal of Mineralogy 11-2, 77 and the

Nifty Copper Mine Nifty Copper Mine is an open pit and underground mining operation in the Great Sandy Desert in the Pilbara region of Western Australia. The mine is located on the traditional land of the Martu people. Overview The open pit extracts copper o ...

, Western Australia.Australian Journal of Mineralogy 12-1, 28 Also in the Kintore open cut at

Broken Hill, New South Wales Broken Hill is a city in the Far West (New South Wales), far west region of outback New South Wales, Australia. An inland mining city, it is near the border with South Australia on the crossing of the Barrier Highway (A32) and the Silver City Hi ...

, Australia, but it is generally inconspicuous there and only a few specimens have been collected.Australian Journal of Mineralogy 3-1, 32 and 50 Material from the Siglio XX Mine,

Llallagua Llallagua (in hispanicized spelling) or Llallawa ( Aymara for a monstrous potato (like two potatoes) or animal, Quechua for the god of seed-time during the Inca period) is a town in the Potosí Department in Bolivia. It is the seat of the Llal ...

, Bolivia, is an unusual pale yellow color, rather than the more common blue or green, forming crusts on

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

and

cassiterite Cassiterite is a tin oxide mineral, SnO2. It is generally opaque, but it is translucent in thin crystals. Its luster and multiple crystal faces produce a desirable gem. Cassiterite was the chief tin ore throughout ancient history and remains ...

, and enclosing crude

octahedral In geometry, an octahedron (: octahedra or octahedrons) is any polyhedron with eight faces. One special case is the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at each vertex. Many types of i ...

jeanbandyite crystals with orange colored shells of plumbogummite.Mineralogical Record 37-2, 127 and 148

References

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External links

The structure of Plumbogummite
Phosphate minerals Lead minerals Trigonal minerals Minerals in space group 166 Crandallite group Minerals described in 1832