Cerussite vs hydrocerussite: how to tell them apart
Cerussite is orthorhombic PbCO3, two good cleavages, density 6.55; hydrocerussite is hexagonal, one perfect {0001} cleavage, 6.80–6.82. The tests, ranked.
Cerussite vs hydrocerussite: read the cleavage first. Cerussite, PbCO3, is orthorhombic with two good cleavages, {110} and {021}, and common twins; hydrocerussite, Pb3(CO3)2(OH)2, is hexagonal with one perfect {0001} cleavage, pearly on it. Density, 6.55 against 6.80–6.82, gives only a 0.11 g gap on a 20 g piece in water. Both fall within hardness 3 to 3.5.
In short
- The decision rule: one cleavage or two. On the two Handbook of Mineralogy sheets, hydrocerussite has a single perfect cleavage, {0001}, with a pearly lustre on it, and thin scaly or tabular crystals; cerussite has two good cleavages, {110} and {021}, conchoidal fracture and common contact twins. One perfect, pearly basal cleavage points to hydrocerussite; twins point to cerussite.
- The optics, if you can measure them. Cerussite is biaxial (−), α 1.803, β 2.074, γ 2.076, 2V 8°–9°. Hydrocerussite is uniaxial (−), ω 2.09, ε 1.94. The birefringence works out at 0.273 against 0.15.
- Documented failure: the balance. Worked as 20 − 20/D, a 20.00 g piece reads 16.95 g in water as cerussite and 17.06–17.07 g as hydrocerussite. A 0.11–0.12 g gap is small enough for matrix, a crack or a bubble to cancel. Hardness does not help either: 3–3.5 against 3.5.
- Documented failure: glow and acid. The cerussite sheet says it may fluoresce yellow under longwave UV; the hydrocerussite sheet prints nothing, so no glow is not evidence. Neither sheet prints an acid reaction, and this page does not use one.
- They grow together. The hydrocerussite sheet names cerussite as an associate at the Mammoth-St. Anthony mine, and by script 4 localities are on both Distribution fields: Leadhills, Tsumeb, the Bunker Hill mine and the Mammoth-St. Anthony mine. A mixed specimen is ordinary, not suspicious.
| Property | Cerussite | Hydrocerussite | Does it separate them? |
|---|---|---|---|
| IMA formula; status, year | Pb(CO3); G, 1845 | Pb3(CO3)2(OH)2; G, 1877 | Yes, by analysis |
| Carbon per lead; lead by mass | 1.000; 77.54% | 0.667; 80.14% | Yes, by analysis |
| System | Orthorhombic; space group Pmcn | Hexagonal; space group n.d. | Yes, with crystals |
| Cleavage | {110} and {021} good; {010} and {012} poor | {0001} perfect | Yes: the first test |
| Lustre | Adamantine, tending toward vitreous, resinous | Adamantine, pearly on {0001} | Yes, on a cleavage face |
| Twinning | Common: {110} stellate or reticulated; {130} heart-shaped | None printed | Yes, when twins are present |
| Habit | Tabular, equant to elongated, pseudohexagonal dipyramidal; crystals to 0.6 m | Steep hexagonal pyramidal to tabular, to 4 cm; lenticular, thin scaly aggregates | Partly: both can look hexagonal |
| Optical class; indices | Biaxial (−); α 1.803, β 2.074, γ 2.076; 2V 8°–9° | Uniaxial (−); ω 2.09, ε 1.94 | Yes, with a microscope |
| Birefringence (worked) | 0.273 | 0.15 | Yes, with a microscope |
| Hardness | 3–3.5 | 3.5 | No |
| Density, measured | 6.55 | 6.80–6.82 | Barely |
| Density from the printed cell | 6.571 (sheet calc. 6.577) | 6.873 (sheet calc. 6.873) | — |
| 20.00 g in water | 16.95 g | 17.06–17.07 g | No: 0.11–0.12 g |
| Tenacity; fracture | Very brittle; conchoidal | Brittle; irregular | Weakly |
| Colour | Colorless, white, pale yellow, smoky to dark gray, black with inclusions | Colorless to white, gray, may display greenish tint | No |
| Luminescence (sheet) | May fluoresce yellow under LW UV | None printed | One way only |
Cerussite vs hydrocerussite: which test should I use first?
Look for cleavage and twins before you reach for a balance: they are the two properties on which the sheets differ in hand specimen. The Handbook hydrocerussite sheet gives one cleavage, {0001}, perfect, with an adamantine lustre that is pearly on {0001}, and crystals that are steep hexagonal pyramids to tabular plates, or lenticular to thin scaly aggregates and cleavable masses. The Handbook cerussite sheet gives two good cleavages, {110} and {021}, two poor ones, conchoidal fracture and very brittle tenacity, and calls twinning common: simple or cyclic contact twins on {110} that make stellate pseudohexagonal or reticulated composites, and contact twins on {130} that make heart-shaped ones.
The rule, stated. A pale, adamantine lead mineral that splits into thin plates along one direction and shows a pearly sheen on that face is a hydrocerussite candidate; one with twinned groups, a conchoidal fracture and no single dominant cleavage is a cerussite candidate. The rule fails on massive or granular material, where neither cleavage nor twins can be seen, and on pseudohexagonal cerussite, which the sheet records. There the answer needs optics or an analysis.
Where the rule comes from. Each line is read off the two sheets; the twin laws and their specimen forms are set out on the cerussite species page, and the hydrocerussite sheet’s full record, with its cell check, on hydrocerussite. Other lead-mineral comparisons are indexed at the collecting guides.
Can a scale tell cerussite from hydrocerussite?
Not reliably: a 20.00 g piece reads 16.95 g in water as cerussite and 17.06–17.07 g as hydrocerussite, a gap of 0.11 to 0.12 g. The figures are worked as 20 − 20/D from the measured densities, 6.55 and 6.80–6.82; the method is how to measure specific gravity at home. Hydrocerussite is 3.8–4.1% denser than cerussite, which is real but small. A trace of matrix, an internal crack or a trapped air bubble moves an in-water reading by that much, and both minerals occur as crusts on matrix. The balance can say that a specimen is a dense lead mineral; it cannot choose between these two.
Why the densities differ, worked. Each printed cell reproduces its sheet’s calculated density. Cerussite’s orthorhombic cell, 5.179 × 8.492 × 6.141 Å with Z = 4, gives 6.571 against the 6.577 printed. Hydrocerussite’s hexagonal cell, (√3/2) × 5.239² × 23.65 Å with Z = 3, gives 6.873, the printed figure. Hydrocerussite carries more lead per formula mass, 80.14% against 77.54%, because each lead carries 0.667 carbonate and 0.667 hydroxyl, lighter in sum than cerussite’s one carbonate per lead.
Hardness does not help. The cerussite sheet gives 3–3.5 and the hydrocerussite sheet 3.5; a scratch test cannot separate a range from its own upper end. The method and its limits are on how to test mineral hardness properly.
Does fluorescence or acid separate them?
Fluorescence works one way at most, and the sheets print no acid test. The cerussite sheet says it may fluoresce yellow under longwave UV. A ligature-aware search of the hydrocerussite sheet finds no luminescence line, while the same search matches the hemimorphite and willemite sheets, its positive controls. A yellow longwave glow is therefore consistent with cerussite, but no glow excludes nothing, because the sheet says may. What other sources print about cerussite’s glow, and which other lead minerals glow yellow, is on is cerussite fluorescent; it is not repeated here.
Acid. Both formulas are carbonates, but neither Handbook sheet prints a reaction with acid, and no source fetched for this page describes one that separates the two. This page therefore gives no acid test. Lead hazards are covered on toxic minerals in a collection and is cerussite toxic; this page is not health or safety advice.
Why do cerussite and hydrocerussite occur together?
The two sheets share four localities and one association line. The hydrocerussite sheet’s association at the Mammoth-St. Anthony mine, Tiger, Arizona, reads cerussite, leadhillite, matlockite, paralaurionite, diaboleite and galena. A script over the two Distribution fields, with each place name checked against the sheet text, finds 4 shared names: Leadhills, Lanarkshire; Tsumeb, Namibia; the Bunker Hill mine, Shoshone Co., Idaho; and the Mammoth-St. Anthony mine. The hydrocerussite sheet lists 15 names and the cerussite sheet 23, the latter as “some of the many localities for fine crystals”, so the overlap is a floor, not a census.
What that means for a label. Cerussite is common in the oxidized zone of lead deposits, per its sheet, and hydrocerussite uncommon in the oxidized portions of lead deposits, per its own. A specimen from Leadhills and Wanlockhead or Tiger carrying both is ordinary. A specimen labelled hydrocerussite from the Mendip ground has a further complication, the hydrocerussite-like somersetite, set out on hydrocerussite.
Who each name is wrong for. Hydrocerussite is the wrong name for twinned or reticulated groups, and for any crystal with two cleavage directions. Cerussite is the wrong name for a thin, pearly, platy crust that cleaves in one direction only. Neither name is right for a massive white lead crust that has not been tested. Nothing on this site is offered for sale; the wanted list is the only commercial route.