Samples from the surface of lava flows discharged by the 2012–2013 Tolbachik Fissure Eruption were found to contain oxysulfates of copper, sodium, and potassium: K
2Cu
3O(SO
4)
2 (fedotovite), NaKCu
2O(SO
4)
2, and Na
3K
5Cu
8O
4(SO
4)
8. The last two phases have no naturally occurring or synthetic analogues that we are aware of. They form flattened crystals of prismatic to long-prismatic habits. The crystals of Na
3K
5Cu
8O
4(SO
4)
8 have a chemical composition corresponding to the empirical formula Na
2.22K
5.47Cu
8.02S
8.05O
36. An X-ray analysis of this compound showed that it has a monoclinic symmetry,
P2/
c,
a = 13.909(4),
b = 4.977(1),
c = 23.525(6) Å, β = 90.021(5)°,
V = 1628.3(7) Å
3. The crystal structure was determined by direct techniques and refined to yield
R 1 for 3955 reflexes//web// with
F 2 > 4σ
F. The compound NaKCu
2O(SO
4)
2 also belongs to the monoclinic system,
P2/
c,
a = 14.111(4),
b = 4.946(1),
c = 23.673(6) Å, β = 92.052(6)°,
V = 1651.1(8) Å
3. The structure was determined by direct techniques to yield a tentative structural model that has been refined up to
R 1 = 0.135 for 4088 reflexes with
F 2 > 4σ
F. The crystal structure of Na
3K
5Cu
8O
4(SO
4)
8 is based on chains of [O
2Cu
4]
4+ consisting of rib-coupled oxy-centered tetrahedrons of (OCu
4)
6+. The chains are surrounded by sulfate radicals, resulting in columns of {[O
2Cu
4](SO
4)
4}
4? aligned along the
b axis. The interchain space contains completely ordered positions of Na
+ and K
+ cations. The principle underlying the connection of NaKCu
2O(SO
4)
2 columns in the crystal structure of {[O
2Cu
4](SO
4)
4}
4? is different, in view of the relation Na:K = 1 as contrasted with 3:5 for the compound Na
3K
5Cu
8O
4(SO
4)
8. The presence of oxy-centered tetrahedrons in the structure of these new compounds furnishes an indirect hint at the importance of polynuclear copper-oxygen radicals with centering oxygen atoms as forms of transport of copper by volcanic gases.
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