massicot

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A solid yellow compound, PbO, which is insoluble in water; m.p. 886°C. It exists in two crystalline forms: litharge (tetrahedral; r.d. 9.53) and massicot (rhombic; r.d. 8.0). It can be prepared by heating the nitrate, and is manufactured by heating molten lead in air. If the temperature used is lower than the melting point of the oxide, the product is massicot; above this, litharge is formed. Variations in the temperature and in the rate of cooling give rise to crystal vacancies and red, orange, and brown forms of litharge can be produced. The oxide is amphoteric, dissolving in acids to give lead(II) salts and in alkalis to give plumbates.

A yellow amorphous powder, the crystalline form of which is litharge; used as a pigment.

Environment

Very rare. Oxidized zones of lead deposits.

Artificial crystals only; natural occurrences are earthy to scaly.

Sulfur to orpiment yellow, sometimes with reddish tint, due to minium (Pb ₃ O ₄ ) impurity. Luster greasy to dull; hardness 2; specific gravity 9.7; cleavage several; powdery or scaly; scales flexible but not elastic; thin scales transparent.

Lead oxide (82.83% Pb, 7.17% O).

Fuses easily to form a yellow glass.

Association with galena is the best guide. Its fusibility without burning like sulfur or giving off arsenic fumes like orpiment should identify it.

Massicot is a secondary mineral, forming on the alteration of galena. Two related minor species, litharge and minimum, form the same way. Massicot usually forms a scaly coating or crumbly film on corroded cavities in that mineral. Litharge (also PbO) has been described as forming the red edge of the massicot scales. Bright red, earthy minium (Pb ₃ O ₄ ) almost never forms scattered crusts on galena or on rock a little farther from the immediate vicinity of the fresh lead sulfide.

Possibly far more common than generally supposed, massicot is dismissed by most mineral collectors as a thin dull coating marring the beauty of their galena specimens. It is found in the old slags of the Greek lead workings at Lavrion, Greece. In Sardinia and in Germany and Hungary it is associated with galena. In Mexico it is reported to occur in fumarolic deposits from two great volcanoes. It has been reported from many U.S. localities, especially in Colorado at Leadville (a source of good minium, too) and in Nevada and California. In Missouri near Potosi, it has been found in the galena associated with the barite of the diggings. Bright red masses of minium from Broken Hill, New South Wales, were the result of a fire roasting cerussite and, though of questionable legitimacy as minerals, are the best specimens available to collectors.