The crystal structure of jensenite, Cu (super 2+) 3 Te (super 6+) O 6 .2H 2 O, has been determined and refined to indices R = 3.3 and R w = 2.5%. The structure is monoclinic, P2 1 /n (14), with cell parameters a 9.224(2), b 9.180(1), c 7.600(1) Aa, beta 102.38(1) degrees , V 628.5(2) Aa 3 , with Z = 4. The structure analysis was essential in determining the valence state of Cu (super 2+) and Te (super 6+) and the number of O (super 2-) atoms and H 2 O groups in the formula. The crystal structure of jensenite contains a sheet of fully occupied edge-sharing [CuO 6 ] and [TeO 6 ] octahedra. These (101) sheets are bonded together through [Cu 2 phi 8 ] dimers (where phi represents either O atoms or H 2 O groups). The dimers contain two H 2 O groups, which reinforce the intersheet linkages via H-bonding. The hexagonal closest packed (HCP) layering in jensenite differs from that in other synthetic and natural cupric tellurates in either the sequence of stacking or the composition of the layers.