Ammineite is the first recognized mineral containing ammine groups. Its formula is [CuCl<sub>2</sub>(NH<sub>3</sub>)<sub>2</sub>]. The mineral is chemically pure. It was found in a guano deposit in Chile. At the same site other ammine-containing minerals were later found:
- Chanabayaite, CuCl(N<sub>3</sub>C<sub>2</sub>H<sub>2</sub>)(NH<sub>3</sub>)÷0.25H<sub>2</sub>O (an alternative formula), a triazolate mineral
- Joanneumite, Cu(C<sub>3</sub>N<sub>3</sub>O<sub>3</sub>H<sub>2</sub>)<sub>2</sub>(NH<sub>3</sub>)<sub>2</sub>, an isocyanurate mineral
- Shilovite, Cu(NH<sub>3</sub>)<sub>4</sub>(NO<sub>3</sub>)<sub>2</sub>
Crystal structure
The characteristic features of the structure of ammineite are:
- layers of trans form of the copper complex, parallel to (001), connected by Cu-Cl bonds
- presence of CuN<sub>2</sub>Cl<sub>4</sub> distorted octahedron ([4+2] coordination)
- edge-sharing of the octahedra produce zigzag chains along the [001] direction
- hydrogen bonds between NH<sub>3</sub> and Cl atoms
Associated minerals
Ammineite coexists with atacamite, darapskite, halite and salammoniac.
Origin
Ammineite is supposed to be a result of an interaction of an earlier copper mineral, likely from a plutonic rock, with ammonia in guano. Ammonia may be produced in decomposition of compounds like urea or uric acid.
References