Plumbogummite is a rare secondary lead
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 ...
, belonging to the
alunite
Alunite is a hydroxylated aluminium potassium sulfate mineral, formula K Al3( S O4)2(O H)6. It was first observed in the 15th century at Tolfa, near Rome, where it was mined for the manufacture of alum. First called ''aluminilite'' by J.C. De ...
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 ...
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 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 r ...
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 o ...
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 with the symbol Ga and atomic number 31. Discovered by French chemist Paul-Émile Lecoq de Boisbaudran in 1875, Gallium is in group 13 of the periodic table and is similar to the other metals of the group ( alum ...
-rich sample of plumbogummite from Tsumeb
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, 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 (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 ...
, 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'' has ...
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 (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 "imitat ...
, 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 an ...
, 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 Gess ...
, 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 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 ...
.[
]
Occurrence
The type locality
Type locality may refer to:
* Type locality (biology)
* Type locality (geology)
See also
* Local (disambiguation)
* Locality (disambiguation)
{{disambiguation ...
is Huelgoat
Huelgoat (; meaning "High Forest") is a commune in the Finistère department of Brittany in northwestern France.
Population
Inhabitants of Huelgoat are called in French ''Huelgoatains''.
Geography
Huelgoat is popular with tourists and holid ...
, Finistère, Brittany, France, and the type material
In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes th ...
is stored in the Natural History Museum, Paris, France.[
Plumbogummite has been found in the Central Cobar Mines, New South Wales, Australia][Australian Journal of Mineralogy 11-2, 77] and the Nifty Copper Mine, Western Australia.[Australian Journal of Mineralogy 12-1, 28] Also in the Kintore open cut 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 i ...
, 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, 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 atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
and cassiterite, and enclosing crude octahedral
In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at ea ...
jeanbandyite crystals with orange colored shells of plumbogummite.[Mineralogical Record 37-2, 127 and 148]
References
{{Reflist
External links
The structure of Plumbogummite
Phosphate minerals
Lead minerals
Trigonal minerals
Minerals in space group 166
Crandallite group