Phosphates, arsenates, vanadates: anions [PO4]3-, [AsO4]3-, [VO4]3- are usually insular; cations may be small with [4] coordination, medium-sized with [6] coordination, or large with [8] or higher coordination; medium-sized cations with octahedral [6] coordination may be insular, corner-, edge- or face-sharing & form major structural units; uranyl phosphates & arsenates, UO2:RO4 = 1:1; UO2+4 tetragonal di-∆ share corners with 4 RO4 tetrahedra, forming continuous sheets in which UO2 surrounded by 4 RO4 in turn surrounded by 4 UO2; these sheets alternate with sheets of divalent cations & H2O molecules.2 Layer pattern is due to strong bonds btw AsO4 radicals & (UO2)O4 polyhedra, which form corrugated tetragonal layers of composition [UO2 (AsO4)]n-n || to (001); these layers are connected mainly by OH—H bonds from H2O molecules in □.3 Zeunerite is isostructural with torbernite & metazeunerite is isostructural with metatorbernite; minerals contain autunite-type sheet of composition [(UO2)(PO4)]-, which involves sharing of equatorial vertices of uranyl □ bi-∆ with phosphate (or arsenate) tetrahedra; in each of these struc-tures, Cu2+ cations are loc btw sheets in Jahn-Teller-distorted (4+2) octahedra with short bonds to 4 H2O grp in □-planar array & 2 longer distances to O atoms of uranyl ions; symmetrically independent H2O grp is held in each structure only by H-bonding, & in torbernite (zeunerite) forms □-planar sets of interstitial H2O grp both above & below planes of Cu2+ cations; in metatorbernite (metazeunerite), □-planar sets of interstitial H2O grp are either above or below planes of Cu2+ cations; bond-length-constrained refinement provided xl chemically reasonable descrip-tions of H-bonding in 4 structures.4