Litharge (from Greek , 'stone' + 'silver' ) is one of the natural mineral forms of
lead(II) oxide, PbO. Litharge is a
secondary mineral which forms from the
oxidation
Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...
of
galena ores. It forms as coatings and encrustations with internal
tetragonal crystal structure. It is dimorphous with the yellow
orthorhombic form
massicot. It forms soft (
Mohs hardness of 2), red, greasy-appearing crusts with a very high
specific gravity of 9.14–9.35. PbO may be prepared by heating lead metal in air at approximately 600 °C (lead melts at only 300 °C). At this temperature it is also the end product of heating of other
lead oxides in air. This is often done with a set of bellows pumping air over molten lead and causing the oxidized product to slip or fall off the top into a receptacle, where it quickly solidifies in minute scales.
:PbO
2 –(293 °C)→ Pb
12O
19 –(351 °C)→ Pb
12O
17 –(375 °C)→ Pb
3O
4 –(605 °C)→ PbO
Historical terminology
Historically, the term ''litharge'' has been combined to refer to other similar substances. For example, litharge of
gold
Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...
is litharge mixed with
red lead, giving it a red color; litharge of bismuth is a similar result of the oxidation of
bismuth; and litharge of silver is litharge that comes as a by-product of separating silver from lead. In fact, ''litharge'' originally meant the mineral residue from silver refining. The term has also been used as a synonym for
white lead or red lead.
Litharge smelting
According to Probert, "
silver
Silver is a chemical element; it has Symbol (chemistry), symbol Ag () and atomic number 47. A soft, whitish-gray, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. ...
ore, litharge (crude lead oxide)
flux and
charcoal were mixed and
smelted in very small
clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...
and stone
furnaces. Resulting silver-bearing lead
bullion was later refined in a second furnace which yielded fine silver, and litharge skimmings which were used again."
[Alan Probert, "Bartolomé de Medina: The Patio Process and the Sixteenth Century Silver Crisis" in Bakewell, Peter, ed. ''Mines of Silver and Gold in the Americas''. Variorum: Brookfield, 1997, pp. 96, .]
References
Further reading
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External links
{{Commonscat
Oxide minerals
Lead minerals
Tetragonal minerals
Minerals in space group 129