cerussite

[German Zerussit, from Latin cērussa, ceruse.]

The mineral form of lead carbonate, PbCO₃. Cerussite is common as a secondary mineral associated with lead ores. In the United States it occurs mostly in the central and far western regions. Cerussite is white when pure but is sometimes darkened by impurities. Hardness is 3¼ on Mohs scale and specific gravity is 6.5. Crystals may be tabular, elongated, or arranged in clusters. See also Carbonate minerals.

Environment

Secondary (weathered) zone of lead ore deposits.

Flat plates common only in small crystals; larger crystals, up to 6 in. (15 cm), usually intergrown into skeletal lattices, like bridge girders (similar to rutile), or in V's as 2 individuals grown together. Often intergrows in the 6-sided habit of a pseudohexagonal bipyramid, like trillings of chrysoberyl. Also massive, and in fragile sprinkles of loosely consolidated needles.

Colorless, white, light yellow to gray; some Tsumeb (Namibia) twins are very dichroic in yellow and violet. Luster adamantine; hardness 3-3Ɖ; specific gravity 6.5-6.6; fracture conchoidal; cleavage good prismatic. Brittle; transparent to translucent; often fluorescent yellow.

Lead carbonate (83.5% PbO, 16.5% CO ₂ ).

One of the most intriguing minerals for blowpiping. Gentle heat turns it yellow to red-brown as it gets hotter and melts. Cools instantly into a faceted crystallized bead. Excessive heat starts rapid reduction to lead. Metal spike is ejected from crystallizing carbonate bead as it solidifies. Make this test; it is one of the most satisfying experiences of blowpipe testing!

The luster, high density, and light color distinguish it from most minerals, and the manner of occurrence distinguishes it from all but anglesite (lead sulfate) and phosgenite (lead chlorocarbonate). The solubility in nitric acid and the fusion behavior distinguish it from the first, the hardness from the latter.

Cerussite is always a secondary mineral that forms from galena through surface alteration, usually when veins of granular and more permeable galena penetrate limestones or dolomites, the carbonate sedimentary rocks. Naturally, its most frequent and best-developed occurrences are where weathering has penetrated deeply, as in desert country. An important ore of lead.

The best and the largest clear crystals have come from Tsumeb, Namibia, associated with malachite, azurite, smithsonite, and anglesite. Good examples were found in the upper levels at the Broken Hill mine, New South Wales. In the U.S., mines in the Organ Mountains, New Mexico, once produced some large V twins, silky white and rust-stained, associated with spectacular wulfenite, anglesite, and vanadinite. Other occurrences are too numerous to list.

Cerussite
Sample of cerussite-bearing quartzite
General
Category	Carbonate mineral
Chemical formula	Lead carbonate: PbCO3
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 crystaline 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-] ≈ 1.5x10^-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

1. ^ http://rruff.geo.arizona.edu/doclib/hom/cerussite.pdf Handbook of Mineralogy
2. ^ http://www.mindat.org/min-934.html Mindat
3. ^ Lightening the Lead Load in Children as cited in Lead Poisoning in Children, and California Poison Control System: Lead Poisoning
4. ^ Gunn, Fenja. (1973). The Artificial Face: A History of Cosmetics. — as cited in Leisure Activities of an 18th Century Lady and Reading Our Lips: The History of Lipstick Regulation in Western Seats of Power

• Mineral galleries
• This article incorporates text from the Encyclopædia Britannica, Eleventh Edition, a publication now in the public domain.

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