Kristjanite, KNa2H(SO4)2, a new fumarolic mineral from Iceland containing the [SO4-H-SO4]3- anion in the crystal structure

Kristjanite, KNa2H(SO4)(2), is a new mineral (IMA2022-131) found in a high-temperature fumarole on Fimmvorouhals,, Iceland. It is monoclinic, P2(1)/n, a = 6.9625(1), b = 9.9953(1), c = 11.0928(2) (angstrom), beta = 105.637(2)degrees and V = 743.40(2) angstrom(3). Kristjanite forms colourless transparent crystals up to similar to 100 mu m in size in compact aggregates with metathenardite, belomarinaite, aphthitalite, ivsite and an unknown mineral with tentative composition KNa2H(SO4)(2), or grows in white globules of smaller grains on their surface. The eight strongest maxima in a powder X-ray diffraction diagram are [d, angstrom (Intensity)] 4.37 (59), 3.65 (32), 3.48 (78), 3.36 (100), 3.18 (76), 2.83 (43), 2.73 (38) and 2.405 (23). The mineral represents a novel crystal structure type. In it, K is coordinated by eight O atoms, and two symmetrically independent Na atoms by seven O atoms. Two symmetrically independent S atoms are in tetrahedral coordination by O atoms. A close to linear, very short hydrogen bond (2.44 angstrom), connects the two to a SO4-H-SO4 dimer. K and Na coordination polyhedra share vertices, edges and even faces forming with sulfate tetrahedra a tight structure with narrow [100] channels lined on two opposite sides by hydrogen bonds.