Zaccagnaite
A zinc-aluminium carbonate-hydroxide forming white hexagons in cavities in Carrara marble.
Intro adapted from Wikipedia (CC BY-SA).
Zaccagnaite is an IMA-recognized mineral species in the carbonate class, with the chemical formula Zn₄Al₂(OH)₁₂(CO₃)·3H₂O.
It crystallizes in the hexagonal crystal system (space group P6_3/mmc). It is a member of the Hydrotalcite structural group.
Key properties: specific gravity 2.82; White streak; Subvitreous to adamantine luster; optically uniaxial.
IMA symbol Zac, IMA status: approved, named in 1997.
Found in cavities in calcite veins in marble formed through alteration of sphalerite by aluminum-rich hydrothermal fluids (Italy). By diagenesis of Zn- and Al-rich ferromanganese speleo-stromatolites (Spain).
It is found associated with Hydrozincite, fraipontite (Italy).
The mineral was named to honor scholar Domenico Zaccagna (1851-1940), who published the first geological map of the Apuan Alps and was a competent collector of minerals from the Carrara marble.