Litharge

Litharge
Litharge structure
General
Category	Oxide minerals
Formula (repeating unit)	PbO
Strunz classification	4.AC.20
Crystal system	Tetragonal
Crystal class	Ditetragonal dipyramidal (4/mmm) H-M symbol: (4/m 2/m 2/m)
Space group	P4/nmm
Identification
Color	red
Cleavage	Distinct/Good. On {110}
Mohs scale hardness	2
Luster	greasy, dull
Diaphaneity	transparent
References

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 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 oxidation of other 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.

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 bismuth is a similar result of the oxidation of bismuth; 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.

According to Probert, "silver ore, litharge (crude lead oxide) flux and charcoal were mixed and smelted in very small clay 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."