Litharge

Litharge is one of the natural mineral forms of lead(II) oxide, PbO. Litharge is a secondary mineral which forms from the oxidation of galena ores. It forms as coatings and encrustations with internal tetragonal crystal structure. It is dimorphous with the 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 approx. 600°C (lead melts at only 300°C). At this temperature it is also the end product of oxidation of other lead oxides in air.^[1] This is often done with a set of bellows pumping air over molten lead and causing the oxidized product to slip/ fall off the top into a receptacle where it quickly solidifies in minute scales.^[2]

PbO₂ –(293 °C)→ Pb₁₂O₁₉ –(351 °C)→ Pb₁₂O₁₇ –(375 °C)→ Pb₃O₄ –(605 °C)→ PbO

Historical terminology

Historically, the term "litharge" has been combined to refer to other similar substances. For example, litharge of gold is litharge mixed with red lead, 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 or red lead.^[3]

References

• Palache, C., H. Berman, and C. Frondel (1944) Dana’s system of mineralogy, (7th edition), v. I, 514–515
• Webmineral data
• Mindat with location data
• Mineral Data Publishing - PDF

1. N.N. Greenwood, A. Earnshaw, "Chemistry of Elements", 2nd edition, Butterworth-Heinemann, 1997.
2. http://chestofbooks.com/health/materia-medica-drugs/Treatise-Therapeutics-Pharmacology-Materia-Medica-Vol1/VI-Semivitrified-Oxide-Of-Lead-Oxide-Of-Lead-Plumbi-Ox.html#.UYdA2crhfU4
3. "litharge". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005. (Subscription or UK public library membership required.)