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Litharge

Litharge

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Litharge is one of the natural mineral forms of lead(II) oxide
Lead(II) oxide
Lead oxide is the inorganic compound with the formula PbO. Lead oxide occurs in two polymorphs, red, having a tetragonal crystal structure and yellow, having an orthorhombic crystal structure...

, PbO. Litharge is a secondary mineral which forms from the oxidation of galena
Galena
Galena is the natural mineral form of lead sulfide. It is the most important lead ore mineral.Galena is one of the most abundant and widely distributed sulfide minerals. It crystallizes in the cubic crystal system often showing octahedral forms...

 ore
Ore
An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element....

s. It forms as coatings and encrustations with internal tetragonal crystal structure
Tetragonal crystal system
In crystallography, the tetragonal crystal system is one of the 7 lattice point groups. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a square base and height .There are two tetragonal Bravais...

. It is dimorphous with the orthorhombic
Orthorhombic crystal system
In crystallography, the orthorhombic crystal system is one of the seven lattice point groups. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a rectangular base and height , such that a,...

 form massicot
Massicot
Massicot is one of the natural mineral forms of lead oxide, PbO. Massicot is the orthorhombic dimorph of the tetragonal form of lead oxide, litharge. It forms soft yellow to reddish-yellow, earthy, scaley masses which are very dense, with a specific gravity of 9.64.It was first described in 1841...

. It forms soft (Mohs hardness of 2), red, greasy-appearing crusts with a very high specific gravity
Specific gravity
Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...

 of 9.14–9.35.

It was first described as a mineral in 1917 for an occurrence in San Bernardino County, California
San Bernardino County, California
San Bernardino County is a county in the U.S. state of California. As of the 2010 census, the population was 2,035,210, up from 1,709,434 as of the 2000 census...

.

Historically, the term "litharge" has been combined to refer to other similar substances. For example, litharge of gold is litharge mixed with red lead
Red lead
Lead tetroxide, also called minium, red lead or triplumbic tetroxide, is a bright red or orange crystalline or amorphous pigment. Chemically, red lead is lead tetroxide, Pb3O4, or 2PbO·PbO2....

, giving it a red color; litharge of silver is litharge that comes as a by-product of separating silver from lead; litharge of bismuth is a similar result of the oxidation of bismuth. The term has also been used as a synonym for white lead
White lead
White lead is the chemical compound 2·Pb2. It was formerly used as an ingredient for lead paint and a cosmetic called Venetian Ceruse, because its opaque quality made it a good pigment. However, it tended to cause lead poisoning, and its use has been banned in most countries.White lead has been...

or red lead.