Massicot is lead (II) oxide mineral with an orthorhombic lattice structure.

Lead(II) oxide (formula: PbO) can occur in one of two lattice formats, orthorhombic and tetragonal.

PbO can be changed from massicot to litharge (or vice versa) by controlled heating and cooling.

At room temperature massicot forms soft (Mohs hardness of 2) yellow to reddish-yellow, earthy, scaley masses which are very dense, with a specific gravity of 9.64.

[8] It may occur as an oxidation product of other lead-bearing minerals such as galena, bournonite, boulangerite, either naturally or in industrial processing.