Cerussite

A specimen of cerussite from Maroc

Cerussite is a Lead Carbonate and an important lead ore.
The name comes from latin cerussa, means white lead.
Cerussite is isomorphous with aragonite.
Like aragonite, it is very frequently twinned (occurs when two separate crystals share some of the crystal lattice points in a symmetrical manner).
Three crystals are usually twinned together on two faces of the prism, producing six-rayed stellate groups with the individual crystal intercrossing at angle of nearly 60 degree.
Usually is colorless or white, sometimes grey or greenish from transparent to translucent and adamantine luster.

Cerussite from certain locations is rich in silver and may be used as minor silver ore.

Uses: lead plaints, lead source and cosmetics throughout history

Characteristics
Group Carbonate - Lead Carbonate
Formula PbCO3
Variable formula: (Pb,Ag,Cr)CO3
Lead 77,54%; Carbon 4,49%; Oxygen 17,96%
Crystal system Orthorhombic
Color: white, colorless, grey, greenish, bluish
Transparent, translucent
Luster adamantine, vitreous, resinous
Habit massive granular, reticulate, tabular to equant crystal
Fracture brittle conchoidal
Hardness: 3-3,75 Mohs
Specific gravity 6,53-6,57
Density 6,58
Streak white
Optical properties biaxial (-)
Rock type: sedimentary, metamorphic
Special characteristics:
Commonly yellow fluorescent under long UV
Disolves with effervescence in dilute nitric acid
Under a blow torch will cause it to fuse very readily and indicate for lead
Insoluble in neutral water but disolves in dilute acids
Breaks down to basci carbonate at about 300 Celsius and turns to decomposes to PbO at 500 Celsius
Decomposes at 204 Celsius acording to reaction: 3PbCo3 = 2Pb2O(CO3)+CO2

Luminescence:
yellowish-white or yellow in long and short wave; intensity weak in long and medium in short UV.
Common activator Pb; other Sm, Ag
Peaks at 515nm; Sm peaks at 564, 597, 649 nm

Crystals of Cerussite glowing yellow in the right photo under long wave UV light

Common mineral associations: Galena, Barite, Azurite, Malachite, Pyromorphite, Sphalerite, Smithsonite, Anglesite, Limonite, Silver, Quartz, Mimetite, Linarite

Distinguishing similar minerals:
Aragonite - lighter in weight, less brilliant in luster, strongly efferverces in hydrochloric acid; cerussite will weakly effervesces in hydrochloric acid
Anglesite - doesn't effervesce at all in hydrochloric acid or disolve in nitric acid and never forms twinned crystals
Phosgenite - softer, fluoresces bright orange
Hemimorphite - harder, not as heavy

Varieties:
Iglesiasite - a variety containing 7% of zinc carbonate, replacing lead carbonate from Iglesias in Sardinia

Other members of this group:
Aragonite CaCO3
Strontianite SrCO3
Witherite BaCO3

Other names: ceruzit ceruzitul ceruzite cerusite cerusitul cerusit cerussite cerrusite cerrussite leas spar plumb white lead ore