Pollucite
A zeolite mineral and major caesium ore.
Pollucite is a zeolite mineral whose chemical makeup is (Cs,Na)2Al2Si4O12·2H2O, often containing iron, calcium, rubidium, and potassium as substitutes. It serves as a major source of caesium and, at times, rubidium. This mineral shares a solid solution relationship with analcime. It forms in the isometric-hexoctahedral crystal system, appearing as colorless, white, gray, or—rarely—pink and blue masses. Well-shaped crystals are uncommon. Its Mohs hardness is 6.5, its specific gravity is 2.9, it fractures brittly, and it lacks cleavage.
August Breithaupt first described pollucite in 1846 from the island of Elba, Italy. The name comes from Pollux, twin of Castor, because the mineral often occurs with petalite (once called castorite). An initial analysis by Karl Friedrich Plattner in 1848 missed its high caesium content; after caesium’s discovery in 1860, a second analysis in 1864 confirmed the element’s abundance in pollucite.
Pollucite typically appears in lithium-rich granite pegmatites alongside quartz, spodumene, petalite, amblygonite, lepidolite, elbaite, cassiterite, columbite, apatite, eucryptite, muscovite, albite, and microcline. Roughly 82% of the world’s known pollucite reserves lie near Bernic Lake in Manitoba, Canada, where it is mined for its caesium content—used in caesium formate for oil drilling assistance. This ore contains about 23% to 25% caesium by weight.
- formula
- (Cs,Na)2Al2Si4O12·2H2O
- crystal_system
- isometric-hexoctahedral
- hardness
- 6.5
- specific_gravity
- 2.9
- color
- colorless, white, gray, rarely pink and blue
- cleavage
- none
- fracture
- brittle
Lore & Background
Pollucite is a zeolite mineral with the chemical formula (Cs,Na)₂Al₂Si₄O₁₂·2H₂O, though iron, calcium, rubidium, and potassium commonly substitute for caesium. It crystallizes in the isometric-hexoctahedral crystal system, typically forming colorless, white, or gray masses; pink and blue varieties are rare, and well-formed crystals are uncommon. The mineral has a Mohs hardness of 6.5 and a specific gravity of 2.9, with a brittle fracture and no cleavage. It forms a solid solution series with analcime. First described by August Breithaupt in 1846 from occurrences on the island of Elba, Italy, it was named after Pollux, the twin of Castor, because it is frequently found alongside petalite, which was previously called castorite. An initial analysis by Karl Friedrich Plattner in 1848 missed its high caesium content, but a second analysis in 1864, following the discovery of caesium in 1860, confirmed the element’s abundance. Pollucite occurs almost exclusively in lithium-rich granite pegmatites, associated with minerals such as quartz, spodumene, petalite, amblygonite, lepidolite, elbaite, cassiterite, columbite, apatite, eucryptite, muscovite, albite, and microcline. It is a significant ore of caesium and sometimes rubidium. Approximately 82% of the world’s known pollucite reserves are located near Bernic Lake in Manitoba, Canada, where it is mined for caesium used in caesium formate for oil drilling assistance; the ore contains about 23% to 25% caesium by weight.
Reader's Guide
Pollucite holds significance as a primary ore of caesium, a metal used in specialized applications such as caesium formate for oil drilling assistance. The mineral's association with lithium-rich pegmatites and its solid solution series with analcime provide insights into geological processes. Economically, the concentration of global reserves near Bernic Lake, Manitoba, makes this deposit critical for caesium supply. The mineral's physical properties—hardness of 6.5, specific gravity of 2.9, brittle fracture, and lack of cleavage—aid in its identification. Its naming after Pollux, twin of Castor, reflects its common association with petalite (castorite).
Did You Know?
- Pollucite is named for Pollux, the twin of Castor, because it is often found associated with petalite (previously known as castorite).
- About 82% of the world's known reserves of pollucite occur near Bernic Lake in Manitoba, Canada.
- Pollucite ore from Bernic Lake is about 23% to 25% caesium by weight.
Frequently Asked Questions
What is Pollucite?
Pollucite is a zeolite-group mineral best known as the principal natural ore of caesium, with occasional rubidium recovery as a byproduct. It is listed as entry 1-24 in the Minerals & Ore Deposits series.
What is Pollucite's chemical formula and how does it relate to other minerals?
Its composition is (Cs,Na)2Al2Si4O12·2H2O, meaning caesium and sodium substitute for one another in the lattice. This allows it to form a continuous solid-solution series with the closely related zeolite analcime.
What crystal system does Pollucite belong to and what are its physical properties?
It crystallizes in the isometric-hexoctahedral system, typically as massive aggregates rather than discrete crystals. Its Mohs hardness is 6.5, specific gravity is 2.9, and it exhibits no cleavage.
What colors can Pollucite appear in?
The vast majority of specimens are colorless, white, or gray, while pink and blue hues are noted as rare variants. These subtle color shifts make unusual specimens a particular draw for collectors.
Why is Pollucite important to industry and mineral enthusiasts?
It is the chief source of caesium, a metal critical to atomic clocks and specialty optics, giving it outsized economic value relative to most zeolites. For hobbyists, its rarity as a caesium-bearing species combined with occasional unexpected coloration makes it a prized cabinet piece.
More in Minerals & Ore Deposits 1-24
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