The crystal structure of wattersite, Hg (super 1+) 4 Hg (super 2+) Cr (super 6+) O 6 , a 11.274(2), b 11.669(2), c 6.603(1) Aa, beta 98.19(2) degrees , V 859.8(3) Aa 3 , space group C2/c, Z = 4, has been solved by direct methods, and refined to an R index of 5.5% based on 1261 unique reflections measured with MoKalpha radiation on an automated four-circle diffractometer. There are three distinct Hg positions in the wattersite structure. Hg(1) is divalent and is coordinated by six atoms of oxygen, forming a distorted octahedron. Hg(2) and Hg(3) form a diatomic Hg (super +) -Hg (super +) bond and are coordinated by three and four oxygen atoms, respectively. Adjacent Hg(1) octahedra share edges and are linked to neighboring CrO 4 tetrahedra, forming chains of composition [HgCrO 6 ] (super 6-) that extend parallel to . These heteropolyhedral chains are linked by O-Hg bonds to the Hg(2)-Hg(3) dimer.