THE MINERAL MASSICOT

Chemical Formula: PbO, Lead Oxide
Class: Oxides and Hydroxides
Uses: As a minor ore of lead, a pigment and as mineral specimens.
Specimens

Massicot, which has been known by the chemically descriptive term of "lead monoxide", is an oxidation product of other lead minerals. It forms under oxidizing conditions of lead ore bodies and its presence is very indicative of the degree of oxidation. Something of interest to petrologists (rock scientists). It is probably more common than is known as it exists as a slight yellowish coating on many lead specimens, often to the detriment of the aesthetic appeal of the underlying mineral.

Massicot is the orthorhombic variety of PbO. The tetragonal variety is the mineral litharge. Both minerals have the same chemistry, PbO, but different structures. Because of this they are called dimorphs ("di" means two and "morph" means shape). Two other much more famous dimorphs are diamond and graphite; both of which are composed of carbon. Litharge is similar to the more common massicot, but the tetragonal structure is apparently lighter than massicot's orthorhombic structure. Litharge is also more orange in color. The two minerals are easily distinguished in petrographic microscopes due to optical differences. It has been found that many crystals of massicot have a fringe of litharge.

THE PHYSICAL CHARACTERISTICS OF MASSICOT:

Color is yellow to reddish yellow due to minium inclusions.
Luster is greasy, earthy to dull.
Transparency: Crystals are generally opaque, but thin scales can be transparent.
Crystal System is orthorhombic; 2 2 2.
Crystal Habits include massive, earthy and scaly coatings on other lead minerals.
Cleavage is distinct in two perpendicular directions, but is rarely seen.
Fracture is uneven.
Hardness is 2.
Specific Gravity is 9.6 - 9.7 (Well above average for any mineral)
Streak is light yellow.
Associated Minerals include minium, galena, barite, wulfenite, pyromorphite, mimetite, bindheimite, cerussite, lead and sphalerite.
Notable Occurrences include Freiberg, Saxony, Germany as well as in Inyo County, California; at the Dogwater Mine, Graham County; Tonopah-Belmont Mine, Maricopa County and Cababi District, Arizona; Potosi, Missouri and at Leadville, Colorado, USA; Sardinia, Italy; Mexico; Hungary; and at Lavrion, Greece.