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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+][CO32-] ≈ 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

References

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1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

CERUSSITE, a mineral consisting of lead carbonate (PbC03), and an important ore of lead. The name (sometimes erroneously spelt cerusite) is from the Lat. cerussa, " white lead." "Cerussa nativa" was mentioned by K. Gesner in 1565, and in 1832 F. S. Beudant applied the name ceruue to the mineral, whilst the present form, cerussite, is due to W. Haidinger (1845). Popular 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 m { 1 IQ}, producing six-rayed stellate groups (figs. and 2) with the individual crystals intercrossing at angles of nearly 60°. Twinning on the faces of the prism r{130}, the angles of which are also nearly 60°, produces a similar kind of grouping, but is much less common. 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. It is usually colourless or white, sometimes grey or greenish in tint; it varies from transparent to translucent, and has an adamantine lustre. It is very brittle, and has a conchoidal fracture. Hardness 3-32; sp. gr. 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. Before the blow pipe it fuses very readily, and gives reactions for lead. Cerussite occurs in metalliferous veins in association with galena, and has been formed by the action of carbonated waters on the galena: it is therefore found in the upper parts of the lodes FIG. 2.

together with other secondary minerals, such as limonite. Finely crystallized specimens have been obtained from the Friedrichssegen mine near Ems in Nassau, Johanngeorgenstadt in Saxony, Mies in Bohemia, Phenixville in Pennsylvania, Broken Hill in 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 772% of lead. (L. J. S.)


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