Massicot

Massicot is the yellow orthorhombic polymorph of lead(II) oxide, with the chemical formula PbO. It is both a mineral that occurs in nature and a historic pigment used in art. As a pigment, massicot provides a bright yellow to orange-yellow hue, and it has also been employed as a precursor in the manufacture of other lead compounds.

Massicot forms in oxidized zones of lead ore deposits, typically as crusts or massive coatings on other minerals. It is commonly associated with minerals such as cerussite (lead carbonate), anglesite (lead sulfate), and galena (lead sulfide). The mineral can occur in tabular to prismatic crystals or as powdery aggregates.

In terms of physical properties, massicot is yellow to orange-yellow in color, with a resinous to earthy luster. It has a relatively low hardness on the Mohs scale (about 2.5) and a high density, around 9.3 g/cm3. It is insoluble in water but dissolves in acids, releasing lead ions. The orthorhombic form (massicot) is one of two common PbO polymorphs; the other, litharge, is tetragonal. The two polymorphs can interconvert under varying temperature and atmospheric conditions.

Uses and safety: Historically, massicot was used as a yellow pigment in oil and tempera paints, and it served as a chemical precursor for other lead compounds. Today its use is restricted due to the toxicity of lead compounds; handling requires caution to avoid inhalation or ingestion of dust and prolonged skin contact.