What is Zirconolite?
Zirconolite is a dense calcium zirconium titanium oxide found in alkaline and mafic rocks, important to collectors for dark lustrous grains and to geoscientists for its ability to host uranium and thorium.
Mineralogy and structure
Reference formula: CaZrTi2O7. Zirconolite is an orthorhombic mineral with ideal formula CaZrTi2O7, but several polytypes and compositional substitutions are known. The Guide uses a labelled natural representative structure rather than implying every zirconolite grain has one identical lattice. Zirconolite is classified with oxides and has orthorhombic crystal symmetry. Typical hardness is 5–6 on the Mohs scale and specific gravity is approximately 4.3–4.6.
Colour, lustre and habit
Typical colours include black, brown, reddish brown, red. The usual granular, massive, tabular habit and adamantine, greasy, sub-metallic lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Zirconolite forms in or is associated with alkaline and mafic igneous rocks, carbonatites, metamorphic rocks and accessory-mineral assemblages. Important documented localities include Norway, Russia, Australia, Canada, Madagascar and alkaline complexes worldwide.
A dark oxide with a nuclear-scale story
Zirconolite rewards serious collectors: the dark, compact appearance hides a technologically important structure capable of preserving radioactive-element signatures over geological time.
Collecting and care
Dense and brittle; treat uranium- or thorium-bearing material as a mineral specimen, avoid dust and grinding, and retain analytical data with the sample.
