Litharge

Litharge (from Greek lithargyros, lithos 'stone' + argyros 'silver' λιθάργυρος) 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 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.

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