What is Cerussite?
Cerussite is an important mineral and significant ore of lead. It is chemically a mineral made up of lead carbonate (PbCO3) and the cerussite ore is a significant ore of lead. The name of the mineral is derived from the Latin word cerussa, which means white lead. The commonly used names of the cerussite ore during early discovery and excavation are lead-spar and white-lead-ore used by the miners in the mining industry. The present form of the cerussite ore terminology is the one given by W. Haidinger, an Australian mineralogist in 1845. An image of the crystal of cerussite mineral is shown below:
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Cerussite Properties and Characteristics
The crystallisation of cerussite gemstone or cerussite stone leads to an orthorhombic system and is isomorphous with aragonite. The aragonite is a very frequently twinned crystal. According to mineralogy, when two separate crystals have crystal lattice points in a similar manner, it is known as crystal twinning. Due to crystal twinning there is an intergrowth of the two separate crystals in different specific configurations. Hence, the type of twinning becomes an identification factor for a mineral. Hence, as mentioned above like the aragonite crystal, the cerussite mineral or cerussite gemstone show twinning and the compound crystal forms of the cerussite mineral, are pseudo-hexagonal in formation.
Some of the Physical Properties of Cerussite Gemstone/Mineral is Listed Below:
The Cerussite crystal formation process includes twinning which gives it a typical pattern which is also an identification factor of the mineral. In cerussite, three crystals are twinned together, on the two faces of the prism. This results in a six-rayed stellate group in which the individual crystals are intercrossing at angles of nearly 60°.
These crystals are very bright and have smooth faces. Most of the cerussite crystals found show these physical properties of brightness and smoothness.
Cerussite mineral occurs in two different types of forms. They are: compact granular masses form and fibrous forms. Both the forms are adequately found at their specific mineral sites.
The mineral is also known for being colorless or white, although sometimes it may contain grey or greenish tint and can vary from being transparent to translucent along with an adamantine lustre.
The structure of the mineral does not follow any natural planes of separation and because of this it is brittle and breaks with a conchoidal fracture i.e. with smooth and curved surfaces typically slightly concave and showing concentric undulations.
The specific gravity of the mineral is 6.5.
For testing of the mineral it can be recognised as it dissolves in nitric acid with effervance. A blow-pipe test causes it to fuse rapidly and gives the indication of the presence of lead in the mineral.
Forms and Locations of Cerussite Mineral
Finely crystallized specimens have been obtained from the Friedrichssegen mine in Lahnstein in Rhineland-Palatinate, Johannegeorgenstadt in Saxony, Stribo in Czech Republic, Phoenixville in Pennsylvania, Broken Hill in New South Wales, and other different localities. Acicular (fine needle-like) crystals that are delicate and are of considerable length were found in Pentire Glaze mine near St. Minver in Cornwall. The mineral can also be found at sites where there is a mixture of crystals such as cerussite barite galena, which are crystals made up of lead, barium and galena, respectively.
Cerussite is often found in quantities with a lead content of upto 77.5%. There is also a variety of cerussite containing 7% of zinc carbonate instead of lead carbonate and this mineral form is known as Iglesiasite, from Iglesias in Sardinia, where it is found. Lead (II) carbonate which is the main component of the mineral is practically insoluble in neutral water, but will not dissolve in dilute acids.
Usage of Cerussite
“White lead”, the common name of cerussite, has been a main ingredient in the preparation of lead paints. These paints have been used in oil-paints that have been used for house paintings or in art exhibition paintings, and also in water based paints. But as the use of lead paints decreased because of the increasing lead poisoning cases in children due to the ingestion of lead-based paint chips. Along with paints, both the “white lead” and lead acetate have been used very commonly in cosmetics throughout history but the current trends have shown decreased or ceased in the lead-based cosmetic applications at least in western countries.
FAQs on Cerussite
1. What is Cerussite and what is its chemical formula?
Cerussite is a mineral consisting of lead carbonate. It is an important and common secondary ore of lead, often referred to as "white lead ore" due to its typical colour. Its chemical formula is PbCO₃.
2. What are the main industrial uses of Cerussite?
The primary use of Cerussite is as an ore of lead. Historically, lead extracted from it was used in paints, which is why it is also known as "white lead ore." Today, its use in consumer products is heavily restricted due to its toxicity, but it remains a significant source for extracting lead for industrial applications like car batteries, radiation shielding, and alloys.
3. What key physical properties help in identifying Cerussite?
Cerussite can be identified by several distinct physical properties:
- Colour: It is typically colourless, white, or grey, but impurities can make it appear blue or green.
- Lustre: It has an adamantine (diamond-like) or vitreous (glassy) lustre.
- Hardness: It is quite soft, with a Mohs hardness of only 3 to 3.5.
- Specific Gravity: It is exceptionally dense for a non-metallic mineral, with a high specific gravity of around 6.5, making it feel very heavy for its size.
- Crystal Form: It often forms complex and twinned crystals, creating intricate lattice-like structures.
4. Is it dangerous to handle or touch Cerussite?
Yes, Cerussite is toxic and must be handled with care. It contains a high percentage of lead, a heavy metal that can cause lead poisoning if its dust is inhaled or if particles are ingested. While brief skin contact is not highly dangerous, it is crucial to wash hands thoroughly after handling any specimens and to avoid creating or breathing in dust from the mineral.
5. How is Cerussite formed in the environment?
Cerussite is a secondary mineral, meaning it forms from the alteration of a pre-existing mineral. It is created in the upper, oxidized zones of lead ore deposits when the primary lead ore, Galena (PbS), comes into contact with carbonated water. The chemical reaction between the Galena and the carbonic acid in the water results in the formation of lead carbonate, or Cerussite.
6. How does Cerussite differ from Galena as an ore of lead?
The primary difference between Cerussite and Galena lies in their chemical composition and origin, which is a key concept in metallurgy as per the CBSE syllabus.
- Composition: Cerussite is a lead carbonate ore (PbCO₃), while Galena is a lead sulfide ore (PbS).
- Origin: Cerussite is a secondary mineral formed by the weathering of Galena. Galena is the primary ore, formed during the original geological event.
- Extraction: This chemical difference necessitates different extraction methods. Cerussite (a carbonate ore) is processed using calcination, while Galena (a sulfide ore) undergoes roasting.
7. How is metallic lead extracted from Cerussite ore?
The extraction of lead from Cerussite aligns with the principles of metallurgy taught in the NCERT curriculum and involves two main steps:
1. Calcination: The Cerussite ore (PbCO₃) is heated intensely in a furnace with a limited supply of air. This thermal decomposition breaks it down into lead(II) oxide (PbO) and releases carbon dioxide gas.
2. Smelting: The lead(II) oxide is then mixed with a reducing agent, like coke (carbon), and heated in a blast furnace. The carbon reduces the lead oxide to molten metallic lead (Pb).
8. Why does some Cerussite glow under UV light?
The ability of Cerussite to glow, or fluoresce, under ultraviolet (UV) light is due to the presence of specific trace elements or impurities within its crystal lattice that act as activators. When UV light strikes the mineral, these activators absorb the energy, causing their electrons to jump to a higher energy state. As the electrons immediately fall back to their normal state, they release this energy as visible light, creating the glowing effect, which is typically a creamy yellow or white colour.
