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Figure 2
The structures formed by four-connected networks, involving (II)–(VI), (III)–(V) and (IV)–(IV) pairs of atoms. (a) The structure of β-BeO. (b) Perspective view of the tetrahedral B network in CrB4 (Cr atoms as green spheres). (c) The AlSi network in anorthite (CaAl2Si2O8). Ca atoms are lodged in the octagonal tunnels. (d) The AlP subarray of variscite AlPO4·2H2O. Note the similarity with the HP-Si of Fig. 1[link](b). The Al and P atoms form the puckered 4.82 layers. (e) The AlP subarray in metavariscite. Note the differences in the stacking of the 4.82 layers in variscite and, at the same time, the similarities with both anorthite and β-BeO. (f) An isolated puckered 4.82 layer to show its differences with the networks of HP-Si represented in Fig. 1[link](e).

Journal logoSTRUCTURAL SCIENCE
CRYSTAL ENGINEERING
MATERIALS
ISSN: 2052-5206
Volume 65| Part 1| December 2009| Pages 11-21
doi:10.1107/S010876810803423X
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