Massicot

Massicot
Massicot from the Monte Cristo mine, Goodsprings District, Clark County, Nevada (size: 5.0 x 4.0 x 4.0 cm)
General
Category	Oxide mineral
Formula (repeating unit)	PbO
Strunz classification	4.AC.25
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pbcm
Unit cell	a = 5.4903 Å, b = 5.892 Å, c = 4.752 Å; Z = 4
Identification
Color	Yellow may have a red tint
Crystal habit	Scaly as incrustations, massive
Cleavage	Distinct on {100} and {010}
Fracture	Flexible
Mohs scale hardness	2
Luster	Greasy to dull
Streak	Yellow
Diaphaneity	Translucent
Specific gravity	9.642 calculated
Optical properties	Biaxial (+)
Refractive index	nα = 2.510 nβ = 2.610 nγ = 2.710
Birefringence	δ = 0.200
Pleochroism	Y = light sulfur-yellow; Z = deep yellow
2V angle	Measured: 90°, calculated: 86°
Dispersion	Strong
References

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. The tetragonal form is called litharge. 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. Massicot can be found as a natural mineral, though it is only found in minor quantities. In bygone centuries it was mined. Nowadays massicot arises during industrial processing of lead and lead oxides, especially in the glass industry, which is the biggest user of PbO.

The definition of massicot as orthorhombic PbO dates from the 1840s, but the substance massicot and the name massicot has been in use since the late medieval era. There is some evidence that the ancient Romans used the substance.

It may occur as an oxidation product of other lead-bearing minerals such as galena, bournonite, boulangerite, either naturally or in industrial processing. When massicot is found in a natural environment, some other minerals that may be found with it may include cerussite, litharge, minium, wulfenite, oxides of antimony and limonite.