Kröhnkite ( Na2Cu(SO4)2•2H2O ) is a rare copper sulfate mineral named after B. Kröhnke who first researched it.

[6] It also has a unique motif of sulfate tetrahedra chains and copper octahedra aligned along the c axis and linked together by sodium atoms.

[5] Kröhnkite exhibits the optical property birefringence; the difference in the two refractive indices of a mineral.

[7] Kröhnkite was first researched after an occurrence in the Chuquicamata Mine, Chile, and has been reported from a number of locations in the Atacama region.

Associated minerals in the discovery location include atacamite, blodite, chalcanthite, antlerite and natrochalcite.