Plumbogummite
Encyclopedia
Plumbogummite is a rare secondary lead phosphate mineral, belonging to the alunite
supergroup of minerals, crandallite subgroup. Some other members of this subgroup are:
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.
Mills et al. investigated a gallium
-rich sample of plumbogummite from Tsumeb
, Namibia, and found larger cell parameters, with a = 7.0752 Å and c = 16.818 Å.
, kidney shaped, stalactitic or globular crusts or masses, frequently with a concentric structure; rare crystals have a hexagonal
outline. Pyromorphite and baryte are common associated minerals, and plumbogummite may be pseudomorph
ic after them. Other associated minerals include mimetite
, duftite
, cerussite
, anglesite
and wulfenite
.
, Finistère, Brittany, France, and the type material is stored in the Natural History Museum, Paris, France.
Plumbogummite has been found in the Central Cobar Mines, New South Wales, Australia and the Nifty Copper Mine, Western Australia. Also in the Kintore open cut at Broken Hill, New South Wales
, Australia, but it is generally inconspicuous there and only a few specimens have been collected.
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
and cassiterite
, and enclosing crude octahedral jeanbandyite crystals with orange colored shells of plumbogummite.
Alunite
Alunite is a sulfate mineral that was first observed in the 15th century in Monti della Tolfa, north of Rome, where it was mined for the manufacture of alum. First called aluminilite by J.C. Delamétherie in 1797, this name was contracted by François Beudant in 1824 to alunite.Distinct crystals of...
supergroup of minerals, crandallite subgroup. Some other members of this subgroup are:
- Crandallite, CaAl3(PO4)2(OH)5·H2O, where calcium replaces lead
- Goyazite, SrAl3(PO4)(OH)5·H2O, where strontium replaces lead
- Philipsbornite, PbAl3(AsO4)2(OH)5·H2O, where the arsenateArsenateThe arsenate ion is AsO43−.An arsenate 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]....
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 parameters (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
Gallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...
-rich sample of plumbogummite from Tsumeb
Tsumeb
Tsumeb is a city of 15,000 inhabitants and the largest town in Oshikoto region in northern Namibia. Tsumeb is the home of the world-famous Tsumeb mine, and the "gateway to the north" of Namibia. It is the closest town to the Etosha National Park...
, 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, 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 botryoidalBotryoidal
A botryoidal texture or mineral habit is one in which the mineral has a globular external form resembling a bunch of grapes as derived from the Greek. This is a common form for many minerals particularly hematite where it is the classically recognized shape. It is also a common form of goethite,...
, kidney shaped, stalactitic or globular crusts or masses, frequently with a concentric structure; rare crystals have a hexagonal
Hexagonal crystal system
In crystallography, the hexagonal crystal system is one of the 7 crystal systems, the hexagonal lattice system is one of the 7 lattice systems, and the hexagonal crystal family is one of the 6 crystal families...
outline. Pyromorphite and baryte are common associated minerals, and plumbogummite may be pseudomorph
Pseudomorph
In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form , resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced by another...
ic after them. Other associated minerals include mimetite
Mimetite
Mimetite, whose name derives from the Greek Μιμητής mimethes, meaning "imitator", is an arsenate mineral which forms as a secondary mineral in lead deposits, usually by the oxidation of galena and arsenopyrite. The name is a reference to mimetite's resemblance to the mineral pyromorphite...
, duftite
Duftite
Duftite is a relatively common arsenate mineral with the formula CuPb, 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 conichalcite specimens from Tsumeb are commonly zoned in...
, cerussite
Cerussite
Cerussite is a mineral consisting of lead carbonate , and an important ore of lead. The name is from the Latin cerussa, white lead. Cerussa nativa was mentioned by Conrad Gessner in 1565, and in 1832 F. S. Beudant applied the name cruse to the mineral, whilst the present form, cerussite, is due to...
, anglesite
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 celestine. It contains 74% of lead by mass and...
and wulfenite
Wulfenite
Wulfenite is a lead molybdate mineral with the formula PbMoO4. 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 it is sometimes called "yellow lead ore".It crystallizes...
.
Occurrence
The type locality is HuelgoatHuelgoat
Huelgoat is a commune in the Finistère department of Brittany in northwestern France.-Population:Inhabitants of Huelgoat are called in French Huelgoatains.-Geography:...
, Finistère, Brittany, France, and the type material is stored in the Natural History Museum, Paris, France.
Plumbogummite has been found in the Central Cobar Mines, New South Wales, Australia and the Nifty Copper Mine, Western Australia. Also in the Kintore open cut at Broken Hill, New South Wales
Broken Hill, New South Wales
-Geology:Broken Hill's massive orebody, which formed about 1,800 million years ago, has proved to be among the world's largest silver-lead-zinc mineral deposits. The orebody is shaped like a boomerang plunging into the earth at its ends and outcropping in the centre. The protruding tip of the...
, Australia, but it is generally inconspicuous there and only a few specimens have been collected.
Material from the Siglio XX Mine, Llallagua
Llallagua
Llallagua is a town in the Potosí Department in Bolivia. It is the seat of the Llallagua Municipality, the third municipal section of the Rafael Bustillo Province.- External links :*-References:*...
, Bolivia, is an unusual pale yellow color, rather than the more common blue or green, forming crusts on quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
and cassiterite
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...
, and enclosing crude octahedral jeanbandyite crystals with orange colored shells of plumbogummite.