| Structural type | A8 |
| Common name | grey-selenium |
| Definition | distortion of sc towards 2-fold coordination |
| Prototype | grey-Se |
| Pearson symbol | hP3 |
| Space group | 152 P3121 D36 |
| Chemical formula | A |
| Bonding | covalent within the polymer |
| Atomic positions | A (3a) xi 0 1/3 |
| Coordination | 2+4 (6ap), see the figure below |
| PDB files | A8 at ξ=1/3 as sc, A8 at ξ=1/2 at ideal packing |
| Parameters | c/a, 0<ξ<1/2 (see the figure below for precise range, other ξ can be reduced to ξ<1/4) |
| Superstructures | graphite layers in eclipsing stacking for ξ=0, sr for ξ=1/3, in particular sc for c/a=sqrt(3/2), 180 P6222 symmetry for ξ=1/2 |
| Substances | VI elements |
