What is Zaratite?
Zaratite is the traditional name for an emerald-green secondary nickel carbonate coating, attractive in hand specimen but scientifically important because its identity and composition can be variable.
Mineralogy and structure
Reference formula: Ni3CO3(OH)4·4H2O. The traditional formula is Ni3CO3(OH)4·4H2O, but modern work has shown that material sold or labelled as zaratite may be low-crystalline zaratite-like material, nullaginite or gaspéite. No artificial lattice is shown for this questionable, poorly crystalline record. Zaratite is classified with carbonates and has isometric crystal symmetry. Typical hardness is 3–3.5 on the Mohs scale and specific gravity is approximately 2.57–2.65.
Colour, lustre and habit
Typical colours include emerald green, green. The usual botryoidal, crusty, massive habit and vitreous, greasy lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Zaratite forms in or is associated with oxidation of nickel sulfides and ultramafic rocks, especially in humid secondary zones. Important documented localities include Galicia in Spain, New Caledonia, Tasmania and nickel districts in the United States.
A green coating where identification matters
Zaratite is a useful lesson in responsible collecting: the intense green colour attracts buyers, but a premium specimen is one with honest locality, careful naming and analytical support.
Collecting and care
Soft and chemically sensitive: avoid acids, soaking and abrasion. Preserve the host rock and provenance, and do not sell a green coating as confirmed zaratite without analysis.
