Ammineite

Ammineite
Sky blue ammineite crystals (a mineral with amine groups, IMA 2008-032) in a matrix of halite. From: Pabellon de Pica, Chanabaya, Iquique Province, Tarapacá Region, Chile.
General
Category	Chloride mineral
Formula	CuCl2(NH3)2
IMA symbol	Amm [1]
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Cmcm
Unit cell	a = 7.79, b = 10.64 c = 5.84 [Å] (approximated)
Identification
Color	Blue
Crystal habit	Hypidiomorphic crystals; powdery masses
Mohs scale hardness	1
Luster	Vitreous
Streak	Light blue
Specific gravity	2.38 (calculated)
Pleochroism	Dark blue to light blue
References	[2] [3]

Ammineite is the first recognized mineral containing ammine groups. Its formula is [CuCl₂(NH₃)₂]. The mineral is chemically pure. It was found in a guano deposit in Chile. ^{[2] [3]} At the same site other ammine-containing minerals were later found: ^{[4] [5] [6] [7]}

• Chanabayaite, CuCl(N₃C₂H₂)(NH₃)·0.25H₂O (an alternative formula), a triazolate mineral
• Joanneumite, Cu(C₃N₃O₃H₂)₂(NH₃)₂, an isocyanurate mineral
• Shilovite, Cu(NH₃)₄(NO₃)₂

Crystal structure

The characteristic features of the structure of ammineite are: ^[2]

• layers of trans form of the copper complex, parallel to (001), connected by Cu-Cl bonds
• presence of CuN₂Cl₄ distorted octahedron ([4+2] coordination)
• edge-sharing of the octahedra produce zigzag chains along the [001] direction
• hydrogen bonds between NH₃ and Cl atoms

Associated minerals

Ammineite coexists with atacamite, darapskite, halite and salammoniac. ^[2]

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. ^[2]

References

1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi: 10.1180/mgm.2021.43 . S2CID   235729616.
2. Bojar, H.-P., Walter, F., Baumgartner, J., and Färber, G. 2010. Ammineite, CuCl₂(NH₃)₂, a new species containing an ammine complex: mineral data and crystal structure. The Canadian Mineralogist 48(6), 1359-1371.
3. Mindat, Ammineite, http://www.mindat.org/min-38895.html
4. Mindat, Pabellón de Pica, http://www.mindat.org/loc-192704.html
5. Mindat, Chanabayaite, http://www.mindat.org/min-43945.html
6. Mindat, Joanneumite, http://www.mindat.org/min-42755.html
7. Mindat, Shilovite, http://www.mindat.org/min-46139.html