Photo of Cerussite in Processed & Rough Form
Cerussite is a mineral with a hardness of 4 out of 10 on the Mohs scale of mineral hardness [?]. These Orthorhomibicly structured gems are made of lead carbonate, their full chemical compound being PbCO3.
Cerussite is a colorless carbonate of the aragonite mineralogical classification. It appears as colorless or white crystals with grayish tints, elongated and generally twinned to form a reticulated network with 60-degree angles, as stubby, tabular crystals in star- or heart-shaped twins. It can also be grey, greenish, or blue as a result of inclusions, such as lead, or copper. Impure cerussite is earthy and darker.
It is semi-hard, very heavy, very fragile, and has a prismatic cleavage. It ranges from transparent to translucent with an adamantine luster, and exudes a bright blue-green fluorescence in ultraviolet light. When heated, it turns brown, then fuses easily.
It is insoluble in hydrochloric acid, but dissolves in nitric acid, with strong effervescence, distinguishing it from anglesite.
It usually occurs in the oxidation zone of lead deposits, produced by the chemical alteration of galena through the action of waters rich in carbonic acid. It usually forms in the altered parts of mineral veins, with lead, copper, and zinc.
Examples are visible as very large, clear crystals in Tsumeb (Namibia) and Dona Ana (New Mexico). Splendid crystals can be found in Broken Hill (Australia), Rhodesia, Pennsylvania, Colorado, Germany, Czechoslovakia, Tunisia, Siberia, Yugoslavia. In Italy it is commonly found as small, very clear crystals in close bundles at Montevecchio and Monteponi. Sizable deposits are worked in Kasakhstan.
Cerussite is also called "white lead" or "lead spar."
What causes Cerussite's exceptional adamantine luster?
The high refractive indices and strong dispersion result from lead content in the crystal structure. This creates the distinctive adamantine luster and diamond-like optical properties that characterize fine specimens.
How do formation conditions affect crystal habits?
Cerussite forms as a secondary mineral in lead deposit oxidation zones. Environmental conditions during formation determine crystal habit, ranging from prismatic to tabular to acicular. Twinning is common, often producing distinctive reticulated groups.
What explains the frequent crystal twinning?
The orthorhombic crystal system of cerussite promotes specific twinning laws, particularly on {110} and {130}. This results in characteristic cyclic twins and complex reticulated groups prized by collectors.
Why are Broken Hill specimens particularly valued?
Specimens from Broken Hill, Australia, show exceptional crystal development and clarity. These often display complex twinning patterns and outstanding luster, establishing standards for museum-quality specimens.
What analytical methods verify identification?
Diagnostic properties include specific gravity (6.4-6.6), reaction with acids, and distinct optical characteristics. X-ray diffraction provides definitive structural confirmation for scientific analysis.
How does chemical composition affect stability?
The lead carbonate composition makes cerussite sensitive to acidic conditions. Specimens require controlled storage environments to prevent degradation. Natural weathering can produce pseudomorphs after galena.
What causes color variations in Cerussite?
Pure cerussite is colorless, but trace elements and structural impurities can produce gray, white, or brown tints. The most valued specimens show complete transparency with high adamantine luster.
The specific gravity [?] for Cerussite is 6.51, its refractive index [?] is 1.80-2.08, and its double refraction [?] is 0.274.
History
Cerussite takes its name from the Latin "cerussa," meaning "white lead" or "whiting." Cerussa nativa was indicated by Conrad Gessner in 1565, but its present form, cerussite, is from W. Haidinger (1845). In its natural mineral form, cerussite is rarely noted in paintings, but its synthetic counterpart, lead white, is considered to be the most important white pigment since the time of ancient Greece.
Industrial Usages
Cerussite is an ore for lead, and to a lesser extent, silver. It is important for the study of deposits and of interest to collectors. It is sometimes mistaken for diamond, and other colorless or brownish stones. Collectors value the orthorhombic crystals which are frequently twinned to give pseudo-hexagonal shapes.
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