Cerussite

Cerussite
Cerussite, Les Frages Mine – France
General
Category	Carbonate mineral
Chemical formula	Lead carbonate: PbCO3
Strunz classification	05.AB.15
Identification
Color	Colorless, white, gray, blue, or green
Crystal habit	Massive granular, reticulate, tabular to equant crystals
Crystal system	Orthorhombic – Dipyramidal (2/m 2/m 2/m)
Twinning	Simple or cyclic contact twins
Cleavage	Good [110] and [021]
Fracture	Brittle conchoidal
Mohs scale hardness	3 to 3.5
Luster	Adamantine, vitreous, resinous
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	6.53–6.57
Optical properties	Biaxial (-)
Refractive index	nα = 1.803, nβ = 2.074, nγ = 2.076
Birefringence	δ = 0.273
Other characteristics	May fluoresce yellow under LW UV
References	[1][2]

Cerussite (also known as lead carbonate or white lead ore) is a mineral consisting of lead carbonate (PbCO₃), and an important ore of lead. The name is from the Latin cerussa, white lead. Cerussa nativa was mentioned by Conrad Gessner in 1565, and in 1832 F. S. Beudant applied the name cruse to the mineral, whilst the present form, cerussite, is due to W. Haidinger (1845). Miners' names in early use were lead-spar and white-lead-ore.

Cerussite crystallizes in the orthorhombic system and is isomorphous with aragonite. Like aragonite it is very frequently twinned, the compound crystals being pseudo-hexagonal in form. Three crystals are usually twinned together on two faces of the prism, producing six-rayed stellate groups with the individual crystals intercrossing at angles of nearly 60°. Crystals are of frequent occurrence and they usually have very bright and smooth faces. The mineral also occurs in compact granular masses, and sometimes in fibrous forms. The mineral is usually colorless or white, sometimes grey or greenish in tint and varies from transparent to translucent with an adamantine lustre. It is very brittle, and has a conchoidal fracture. It has a Mohs hardness of 3 to 3.75 and a specific gravity of 6.5. A variety containing 7% of zinc carbonate, replacing lead carbonate, is known as iglesiasite, from Iglesias in Sardinia, where it is found.

The mineral may be readily recognized by its characteristic twinning, in conjunction with the adamantine lustre and high specific gravity. It dissolves with effervescence in dilute nitric acid. A blowpipe test will cause it to fuse very readily, and gives indications for lead.

As crystalline ore

Finely crystallized specimens have been obtained from the Friedrichssegen mine in Lahnstein near Nassau, Johanngeorgenstadt in Saxony, Mies in Bohemia, Phoenixville in Pennsylvania, Broken Hill, New South Wales; and several other localities. Delicate acicular crystals of considerable length were found long ago in the Pentire Glaze mine near St Minver in Cornwall. It is often found in considerable quantities, and contains as much as 77.5% of lead.

Lead(II) carbonate is practically insoluble in neutral water (solubility product [Pb²⁺][CO₃^2–] ≈ 1.5×10^–13 at 25 °C), but will dissolve in dilute acids.

Commercial uses

"White lead" is the key ingredient in (now discontinued) lead paints. Ingestion of lead-based paint chips is the most common cause of lead poisoning in children.^[3]

Both "white lead" and lead acetate have been used in cosmetics throughout history, though this practice has ceased in Western countries.^[4]

Crystals of cerussite, a secondary lead ore

See also

• Venetian Ceruse – Cerussite based cosmetic worn by Elizabeth I of England.

References

• Mineral galleries
•  This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press.