What is Zaccagnaite?
Zaccagnaite is a rare hydrated zinc aluminium carbonate of the hydrotalcite supergroup, usually appearing as pale botryoidal or powdery material in altered carbonate environments.
Mineralogy and structure
Reference formula: Zn6Al3(OH)16CO3·4H2O. Zaccagnaite has hydrotalcite-like layered chemistry and variable zinc-aluminium-water content. The ideal formula is Zn6Al3(OH)16CO3·4H2O; a labelled representative COD model is used because natural stacking and hydration can vary. Zaccagnaite is classified with carbonates and has hexagonal crystal symmetry. Typical hardness is 2–3 on the Mohs scale and specific gravity is approximately 2.1–2.4.
Colour, lustre and habit
Typical colours include colourless, white, pale green, pale blue. The usual botryoidal, crusty, granular habit and pearly, vitreous, dull lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Zaccagnaite forms in or is associated with low-temperature alteration in karst, carbonate rocks and zinc-rich oxidation zones. Important documented localities include the Apuan Alps of Italy, Spain, Greece and other zinc-carbonate localities.
Layered chemistry in a pale botryoidal coating
Zaccagnaite appeals to collectors of rare supergroup minerals: the gentle colour and soft texture invite close inspection, while the layered structure gives the specimen real scientific depth.
Collecting and care
Soft and hydrated: keep dry, avoid acids and abrasion, and preserve the carbonate host and locality. Handle powdery coatings minimally.
