Massicot

Massicot is a naturally occurring, relatively rare, yellow-colored mineral form of lead(II) oxide, with the chemical formula PbO. It is one of two known forms of PbO, the other being litharge, which is red or orange. Massicot is orthorhombic in crystal structure, while litharge is tetragonal. The color difference and structural variation between massicot and litharge are due to different arrangements of the Pb and O atoms.

Massicot typically appears as earthy, powdery, or scaly masses and is often found as a weathering product of galena (lead sulfide, PbS) and other lead-bearing minerals. Its formation is generally associated with low-temperature oxidation of lead minerals under oxidizing conditions near the Earth's surface.

Because it is often found in association with other lead minerals, massicot may contain impurities. It has a Mohs hardness of 2 and a relatively high specific gravity of around 9.2.

Massicot has limited commercial uses, primarily due to its rarity and the availability of synthetic lead(II) oxide. Historically, it has been used as a pigment in paint, although its lightfastness can be variable. More commonly, the synthetically produced form of lead(II) oxide is used in the manufacture of lead glass, rubber vulcanization, and other industrial applications. Massicot serves as a valuable indicator mineral for the presence of lead deposits.